The Trouble with Due Dates

One of my clients who is “past due” found this nice article that helped ease her mind. I thought I would pass it along……

Calculating Due Dates and the Impact of Mistaken Estimates of Gestational Age

Janelle Durham, for Certification with Birth Education NW. January, 2002.

Introduction. This paper will examine the methods used by obstetricians to predict the date on which a baby will be born, and also examine how that forecasted due date affects the course of obstetric treatment. Calculating a due date is a very challenging task as many factors go into the equation. First, there’s the question of when the pregnancy began: some women know the date of ovulation or conception, but typically, due dates are based upon the woman’s last menstrual period, a method which carries much potential for error. Second, there’s a question of how long the pregnancy will last. As I discuss in this paper, there’s a great deal of variability in “normal” gestational terms for human babies, so predicting a due date typically has a margin of error of a few weeks on each side of the date.

Psychological and Emotional Effects of Due Dates. The predicted due date has an impact on the psychology of pregnant women and their partners. Although their physician or childbirth educator may have told them that the “due date” is only an estimate, many modern American women take it as a scheduled date around which to make their plans. Some parts of popular culture, like baby betting pools, remind us that the date is difficult to guess; however, other messages imply that we can expect a certain date. The Girlfriend’s Guide to Pregnancy even has a countdown calendar to the due date… there is a token message there saying something like “baby’s not here yet? Well, take care of yourself and be patient.” But clearly the message is to expect the baby then, despite the fact that only 4-5% of babies are born on their exact due date.

In this paper, I will not address this emotional and psychological impact in much detail, but this data should be read with an awareness of this, because it certainly impacts the couples that we work with in childbirth preparation classes. For example, as childbirth educators, we frequently see women who have reached the 38th week of pregnancy, where they’re told the baby is ‘no longer premature’ and the moms are ready for the baby to come. By the time they are past 40 weeks, they are ready for induction, despite knowledge of the risks and side effects of induction.

Medical Decision-Making Based on Due Dates. There are several cases in which medical management of a pregnancy is based on a knowledge of the specific gestational age of the fetus. These include: interpretation of pre-natal test results, determination of the best date for a planned cesarean section, decisions about inducing a ‘post-date’ pregnancy. Errors in estimates of fetal age can lead to further errors, including iatrogenic prematurity, and unnecessary inductions. Despite protocols that have been developed to reduce these errors, some persist, as even physicians can be overly literal in their beliefs about the baby’s due date.

Public Health Record-Keeping. Records of gestational age at birth are used to help determine rates of pre-term births, and to help evaluate the effectiveness of prenatal care. Inaccurate estimates of fetal age could make this information harder to interpret.

How accurate are due dates in the experience of the average American mom?
With the current formula, about 2/3 of babies are born within ten days of their due dates, with approximately 80% of babies born sometime between week 38 and 42 after LMP.

Because visual representation of data is often helpful for illustrating a point, I have included a graph here illustrating the range of dates at which babies are born. The following graph is intended as an illustration of approximately how many births occur within each week of pregnancy. The data on here isnot exact, as it is a composite from multiple sources. I have found multiple references that state that about 6% of babies are pre-term, and that 4-14% of babies would be born after 42 weeks (Odutayo, and others), if it were not for interventions, so the far ends of the scale relate to this data. Galimberti states that 3.5% of labors start spontaneously at 37 weeks, 9.5% at 38 weeks, and 18.5% at week 39. Klimek has an evenly distributed Gauss curve, or bell curve, but does not substantiate it with empirical data. Therefore, my data for weeks 40 and 41 are only estimates, based on a bell curve format.

What is the “normal gestational term” for humans?
Naegele’s Rule: The standard definition for gestational term is 266 days from conception to the date of the baby’s birth. This is also defined as 280 days, or 40 weeks, from the first day of the mother’s last menstrual period, a definition which assumes that the mother ovulates on day 14 of a 28 day menstrual cycle. The formula used to calculate due date is:

(LMP + 7 days) – 3 months = Due Date

This definition is based on observations, first reported by Franz Naegele in 1812, who believed that pregnancy lasted ten lunar months from the last menstrual period. It was not based on empirical data.

Mittendorf’s Observations of Gestational Term. In the 1980’s, Mittendorf noticed that birth dates for women in his practice, primarily second-generation Irish-Americans, averaged seven days past their “due dates”. He reviewed his records, then went on to review records of 17,000 births, and determined the average healthy, white, private-care, primiparous woman averaged 288 days from LMP to birth: 8 days longer than Naegele’s rule. Mittendorf and other researchers have further determined several factors that affect gestational term, including ethnicity, parity, nutrition, substance use, mother’s age, and mother’s size. Based on Mittendorf’s data, a more appropriate formula might be:

(LMP – 3 months) + 15* Days = Due Date
* Add 10, rather than 15, if mother is non-white, or multiparous

Normal Variations in Gestational Term:
From the wide range in birth dates, it is clear that some variation is normal. Some examples of known variations: Multiparous women average 283 days, versus the 288 days of multiparous women. (Mittendorf)  Black women averaged 8.5 days fewer than white women of similar socioeconomic status. (Mittendorf) Other studies indicate that for multiple births, each additional baby in the uterus shortens the pregnancy by 4 weeks on average.

When is a baby physically mature? By standard definitions, 38-42 weeks LMP is normal, before 37 weeks is considered premature and after 42 weeks is considered a post-date pregnancy. Klimek argues that this interpretation may not always be correct. He states if there is this wide of range, then clearly it is normal for some babies to take 38 or fewer weeks to develop to full-term development, when others may take more than 42 weeks to reach maturity. He compares this to the range at which human beings reach puberty, and points out that no one sets a “required” age for puberty, or takes medical steps to induce puberty in ‘late-bloomers.’

Certainly in practice, there are examples which would support this theory. After the baby is born, it is possible to develop Clinical Estimates of Fetal Age.  There are various methods for assessing a baby’s stage of physical development (see appendix for two sample scales). The baby is also weighed and measured, and those numbers are compared to average growth charts.  Medical staff assess babies, and classify them as AGA (appropriate for gestational age) if they’re in the 10th to 90th percentile, or LGA (large for gestational age), or SGA (Small for gestational age) if they are in the outlying ranges. Nurses are taught that babies who are AGA have a better chance for survival than those who are large or small for gestational age, so this helps to establish a general risk factor for the baby. However, by anecdotal evidence, it is clear that some babies born at 37-38 weeks are fully mature by all the criteria on the scale, and other babies born at 42 weeks are just reaching the signs of being mature, “term” infants.

Alaska’s Bureau of Vital Statistics examined data on preterm babies, and compared two measures of gestational age to determine how accurate the reports were: the LMP method and Clinical Estimation of Gestational Age after the birth. “The LMP gestational calculation has a wider distribution (by two weeks) for the 5th and 95th percentiles and a larger standard deviation. Higher levels of very preterm, preterm, and postterm births was shown by the LMP based gestation. A clear preference for a gestational age of 40 weeks was shown by the CE measure. More than 1/3 (35.1%) of births had a CE gestational age of 40 weeks. This compares with 23.2% for the LMP-based measure. Overall, the CE measure classified almost 9 of every 10 births as a term birth.” The difference between the supposed “actual” age of the baby (LMP) and the observed maturity level of the baby could be accounted for partially by errors in determining LMP, but it is also possible that it is due in part to the Klimek’s idea of a normal variation in how long a fetus takes to reach maturity. It is possible that some of the babies who were “premature” by LMP standards tested fine on CE measures simply because of a faster rate of fetal development. Some of the “post-term” babies by LMP standards may have tested as term babies because of a naturally slower rate of development.

Another interesting finding in this study is that “Native infants with an LMP-based gestation of 32 weeks or less showed an average CE gestational age that was from 1 to 3 weeks higher than the comparable group of non-Native infants. The data do suggest that Native infants on average weigh slightly more than non-Native infants, which could partially explain the difference, especially if birth weight was used to help estimate gestation. It could also be that the reported date of last menses is more problematic for Native births.” I would suggest that is might also reflect a shorter average gestational term for Native babies. Although this study did not examine that possibility, a similar variation was seen for African-American babies in Mittendorf’s work, and racial differences may well appear elsewhere.

Summary of gestational term issues. It appears that average length of pregnancy varies significantly from mother to mother, dependent on a variety of factors, not all of which have been studied and explored. This makes due date calculation difficult, even if the exact date of conception were known. However, as we see below, due date prediction is further compounded by uncertainty about when the pregnancy began.

When did pregnancy begin (i.e. when do we start counting gestational age)?
Based on date of conception and/or ovulation. Some women are aware of when they ovulate, either based on formal  methods and record-keeping such as daily temperature checks, or on physical symptoms such as mild pain upon ovulation, or observation of changes in vaginal mucus. Many women know the dates when conception was possible, because they know the dates when they had intercourse during their most recent menstrual cycle. Due dates can be calculated based on these dates, but many physicians prefer to calculate it from date of last menstrual period. They may only calculate from conception date if conception was medically managed and supervised through techniques such as artificial insemination.

Based on date of last normal menstrual period. Due dates are typically calculated based upon the date the last menstrual period began, according to the mother’s report. Naegele’s rule assumes that ovulation occurred 14 days after LMP, which is only the case for women with 28 day cycles. Some caregivers will ask their patients for a history of menstrual cycles so that they can adjust this number, as appropriate, for cycles of different lengths or irregular cycles. It’s also important to consider: recent use of oral contraceptives, and their possible effect on ovulation date; inaccurate memory about when the last period occurred, the possibility of interpreting post-conception ‘spotting’ as a light period, and unrecognized pregnancy losses. These issues all complicate due date prediction, and it’s estimated that nearly 25% of infants who would be classified as preterm birth on the basis of the last normal menstrual period are not preterm. (cited in Health Canada)

Ultrasound: Developing an Estimate of Fetal Age Based on Baby’s Size
Ultrasound can be used to estimate age, by comparing measurements against average fetal growth curves. Crown-Rump Length is measured in the first trimester. Later, they measure the length of the femur, abdominal circumference, head circumference, and diameter across the head (bi-parietal diameter).

Odutayo states that ultrasound is a better method of determining fetal age than LMP. His findings indicate that birth occurred on the due date in 3.6% of cases with LMP dating, and 4.3% of cases where due date was determined by ultrasound. Delivery took place within seven days of the due date for 49.5% of LMP due dates, and for 55.2% of ultrasound due dates. Delivery within ten days of the due date was 64.1% for LMP dates, and 70.3% for ultrasound dates.

Due to these findings, and others: If ultrasound measurements correspond closely to LMP dating, then they are viewed as a confirmation of the LMP date. If ultrasound measurements suggest a significantly different date from the LMP date, many physicians will use the ultrasound date for planning treatment and intervention, rather than using the LMP date. Protocols vary, but generally say that if the dates very by more than one week, or by ten days according to some protocols, especially if LMP is uncertain for any reason, then the ultrasound date is used.

However, because of the significant margin of error in ultrasound measurements, Otto and Platt (1991) argue that the due date should not be changed unless the discrepancy is more than two weeks.

In the first trimester, the margin of error for determining baby’s gestational age is +/- 3-5 days. Therefore, early ultrasounds can often be fairly good indicators of fetal age. However, past the first trimester, babies grow at very different rates, so size is much less accurate for determining fetal age. Up to 20 weeks, the margin of error is +/- 7-10 days. At 20- 30 weeks: +/- 2 weeks. After 32 weeks, fetal age estimates may be up to 3 weeks off in either direction. Therefore, a baby that appears “term” (40 weeks) may be anywhere from 37-43 weeks gestational age.

Other Methods for cross-checking gestational age:
Additional sources of information about baby’s age can be found. Physical estimation of baby’s size can be done by clinical exam and fundal measurement, and then compared to growth charts, similar to the ultrasound method. Quickening: Pregnant women usually first feel fetus move by 16-20 weeks; some believe the baby will arrive 5 months after quickening. Fetal heart tones can indicate gestational age. They can be heard through Doppler starting at 9-12 weeks and by stethoscope at 18-20 weeks. However, a simple summary of our ability to predict due dates is that all clinical dating methods have margins of error of more than two weeks.

Problems with inaccurate due dates / gestational age estimates:
Prenatal Testing. Inaccurate dates can affect the accuracy of  prenatal testing where the interpretation of test results requires a knowledge of the specific gestational age of the baby. For example, if the caregiver has not heard the baby’s heart beat by a certain gestational age, then there may be cause for concern. However, if he is looking for it ‘too early’ because of an error in calculating gestational age, then he may cause un-needed fear and anxiety for the parents.

Another example: the triple screen test (AFP test) is done between 16 and 18 weeks LMP. It measures the levels of protein produced by the fetus, and two pregnancy-produced hormones in the mother’s blood. These levels are compared to where the baby’s levels “should” be at this point in pregnancy, and if discrepancies appear, then further testing, such as amniocentesis may be done to determine the baby’s risk of Down syndrome or other abnormalities. If the fetal age has been misdiagnosed, then the levels will not be appropriately evaluated, and there is a chance that the mother will have an unnecessary amniocentesis, which carries a potential risk to the fetus. (example from Summons, et al)

Iatrogenic Prematurity. In cases of elective cesarean section or medically-indicated induction, a serious risk is iatrogenic prematurity: a baby that is premature because the interventions were performed too early due to error in determining gestational age. This could be prematurity in the more typical sense: if the estimated date of conception (based on LMP) is significantly wrong, then the baby would be delivered prior to 38 weeks of age. It could also be any infant who had not reached full maturity, regardless of weeks of development. “Thus a preterm birth can occur even at the 42nd week just as a postterm birth is possible even at the 38th week.” (Klimek)

Incidence: It has been estimated that 10% of the time the gestational age based on LMP is significantly inaccurate. In some studies, as many as 10% of admissions to neonatal intensive care are due to inadvertent iatrogenic prematurity. (Clewell) Shreiner et al. examined a sample of 47 infants that developed respiratory distress syndrome following elective abdominal delivery “at term.” The mean difference between the gestational age determined pre-natally (by methods such as LMP or ultrasound) and post-natally (by clinical exam) was 2.6 weeks, +/- 1.6 weeks.

Ways to reduce risk: some hospitals and groups (e.g. ACOG, College of Physicians and Surgeons of Manitoba) have established protocols to determine fetal maturity before elective cesarean. These require clear documentation of gestational age based on multiple indicators such as: clear menstrual history, prenatal exam records, Doppler record of fetal heart tone for 30 weeks, more than 36 weeks since a positive urine pregnancy test, and ultrasound estimates of gestational age performed before 20 weeks. If these data are not available, then they recommend amniocentesis: amniotic fluid analysis of the lecithin-to-sphingomyelin (L/S) ratio and phosphatidylglycerol to provide evidence of fetal lung maturity.

Allowing the woman to go into spontaneous labor before c-section would also markedly reduce the risk: The risks of iatrogenic prematurity and lung disease for those infants delivered by elective cesarean before labor are 30 percent versus those born by cesarean after labor begins (11 percent). (PCRM)

Inductions performed for “overdue” babies that are not actually overdue.“Between 4% and 14% (average 10%) of women are prepared to reach 42 weeks gestation, and 2% to 7% (average 4%) to reach 43 weeks gestation depending on the population studied.” (Odutayo) In the overwhelming majority of these pregnancies, the fetus remains healthy, as does the mother.

However, with pregnancies that have passed their 41 week line, physicians become concerned about the baby developing postmaturity syndrome. Some potential concerns: The placenta, which supplies babies with the nutrients and oxygen from the mother’s circulation, begins to age toward the end of pregnancy, and may not function as efficiently as before. Amniotic fluid volume may decrease and the fetus may stop gaining weight or may even lose weight.  Problems may occur during birth if the baby is large. Postmature babies may be at risk for meconium aspiration, when a baby breathes in fluid containing the first stool.  Hypoglycemia (low blood sugar) can also occur because the baby has too few glucose-producing stores.

Due to concerns about postmaturity, many physicians have a standard policy of inducing labor at a certain gestational age. Labor is induced in more than 13% of deliveries in the U.S., and post-date pregnancy is the most common reason for induction. This is despite the fact, as Nichols (1985) states: studies of management have not found that tests accurately identify postmature babies or that routine induction improves perinatal outcome. And, according to ACOG, 95% of babies born between 42 and 44 weeks are born safely. Only a small percentage of pregnancies that last beyond 42 weeks result in babies with post-maturity syndrome. These numbers may reflect issues addressed above: the period for normal prenatal development for a human infant appears to span several weeks. Some so-called late babies may merely have been slow to develop, and are born at the term that is appropriate to their development.

So, there is some question whether it is appropriate to induce labor at 42 weeks of gestation, and this issue is further complicated by all the concerns about inaccurate dating of conception, as described above.

Nichols (1985b) states that 70% of women classified as postdate in his study were incorrectly dated. If the choice to induce is based on menstrual dating, this is likely to result in a high proportion of unnecessary inductions. “In studies where conception has been estimated from basal body temperature charts, and ultrasound measurements, it has been shown that the error in menstrual dating is heavily skewed to the right – i.e., there is a tendency to overestimate gestation.” (Odutayo)

Ultrasonography in the first half of pregnancy could reduce the number of pregnancies classified as >42 weeks from 11.5 to 3.5 (i.e., by 70%). (Odutayo)

However, even with multiple methods for dating the pregnancy, there is still a margin for error in determining the age of the baby, and further questions regarding the age at which this particular baby will reach obstetrical maturity.

Therefore, some research based protocols for post-date pregnancy recommend that with late date pregnancy, tests may be started to evaluate the mother and fetus for signs of postmaturity. Tests include fetal movement counting, ultrasound examination, non-stress test, contraction stress test, and estimation of the amount of amniotic fluid. If these indicate potential postmaturity, the doctor can perform amniocentesis to check for meconium staining of the amniotic fluid before pursuing labor induction. If the fetal well-being tests do not detect signs of postmaturity, a post-date pregnancy may be allowed to continue until labor begins spontaneously.

Teaching Gestational Age and Due date information to students:

How I cover this information in a class series. In the first class, when discussing Onset of Labor, I address due dates, and the question of “When will my Baby Arrive?” I explain briefly how due dates are calculated, and have them calculate their due date if their pregnancy lasted Mittendorf’s 288 average days rather than Naegele’s 280 days. I then point out that if they reach a point where their doctor-determined due date has passed, and they are frustrated and ready for the baby to come, they should remember Mittendorf’s rule, and try not to get impatient yet.

Once this concept has been introduced, students have some knowledge of the normal range of pregnancy length and the problems with estimating fetal age. I can then refer back to this as reminder and reinforcement of the concept in later classes, when talking about: induction risks and alternatives, post-date pregnancies, and the emotional frustrations of late pregnancy when parents, especially mothers, are ready for pregnancy to end, and parenting to begin.


Alaska Bureau of Vital Statistics. “A Comparison of Gestational Age Information Derived from the Birth Certificate, 1990-1998.”
Clewell, William H. “Fetal Lung Maturity Testing.” Arizona Society of Pathologists’ Newsletter.
Children’s Hospital of Pittsburgh website. Postmaturity: The High Risk Newborn.
The College of Physicians and Surgeons of Manitoba, revised 1995. “Prevention Of Iatrogenic Prematurity”
Devoe, LD; Sholl, JS. “Postdates pregnancy. Assessment of fetal risk and obstetric management.” Journal of Reproductive Medicine, 28(9): 576-80. 1983.
Galimberti, A. “Neonatal respiratory morbidity following delivery by elective caesarean section at term: an audit and a review.”
Harman, Jefferson H. and Andrew Kim. “Current Trends in Cervical Ripening and Labor Induction” American Family Physician, August, 1999.
Health Protection Branch, Health Canada. “Pre-term Birth” in “Measuring Up: A Health Surveillance Update on Canadian Children and Youth.”
Isidro-Cloudas, Terry. “Pregnancy past your due date” on
Klimek, Rudy, “The use in obstetrics of quantum theory as well as modern technology to decrease the morbidity and mortality of newborns and mothers during iatrogenic induced delivery” Neuroendocrinology Letters, 2001.
Klimek M. “Prediction of the birth term and course of the labor.” Archives of Perinatal Medicine, 7(3):24-29, 2001
Merck. “The Merck Manual Home Edition.”
Mittendorf, et al. “The Length of Uncomplicated Human Gestation”
Obstetrics & Gynecology, V.75, N.6, June 1990 pp. 929-932.
Parilla, BV; Dooley, SL; Jansen, RD; Socol, ML. “Iatrogenic respiratory distress syndrome following elective repeat cesarean delivery.” Obstetrics and Gynecology, 81(3): 392-5. 1993.
Physician’s Committee for Responsible Medicine, “When is Surgery Unnecessary?”
Schreiner, RL; Stevens, DC; Smith, WL; Lemons, JA, Golichowski, AM; Padilla, LM. “Respiratory Distress following elective repeat cesarean section.”American Journal of Obstetrics and Gynecology, 143(6): 689-92. 1982.
Simkin, Penny. “How Long is too long?” Childbirth Forum, Spring 1993.
Summons, Peter, Warwick Giles and Greg Gibbon. “Decision Support for Fetal Gestation Age Estimation” from the Proceedings of the 10th Australasian conference on Information Systems, 1999.
Wagner, Marsden. “Being Seduced to Induce: What women should know about their OBs.” Excerpted from Midwifery Today E-News, notes from a lecture in New York City, April 2001.
“When will my baby be born?” found at

Dubowitz/Ballard Exam for Gestational Age

Neuromuscular Maturity

Posture: With the infant supine and quiet, score as follows:
  • Arms and legs extended = 0
  • Slight or moderate flexion of hips and knees = 1
  • Moderate to strong flexion of hips and knees = 2
  • Legs flexed and abducted, arms slightly flexed = 3
  • Full flexion of arms and legs = 4
Square Window: Flex the hand at the wrist. Exert pressure sufficient to get as much flexion as possible. The angle between the hypothenar eminence and the anterior aspect of the forearm is measured and scored: >90 degrees = –1; 90º = 0; 60º = 1; 45º = 2; 30º = 3; 0º = 4
Arm Recoil: With the infant supine, fully flex the forearm for 5 seconds, then fully extend by pulling the hands and release. Score the reaction:
  • Remains extended 180 degrees, or random movements = 0
  • Minimal flexion, 140-180 degrees = 1
  • Small amount of flexion, 110-140 degrees = 2
  • Moderate flexion, 90-100 degrees = 3
  • Brisk return to full flexion,
Popliteal Angle: With the infant supine and the pelvis flat on the examining surface, the leg is flexed on the thigh and the thigh fully flexed with the use of one hand. With the other hand the leg is then extended and the angled scored: 180º = -1; 160º = 0; 140º = 1; 120º = 2; 100º = 3; 90º = 4;
Scarf Sign: With the infant supine, take the infant’s hand and draw it across the neck and as far across the opposite shoulder as possible. Assistance to the elbow is permissible by lifting it across the body. Score according to the location of the elbow:
  • Elbow reaches or nears level of opposite shoulder = -1
  • Elbow crosses opposite anterior axillary line = 0
  • Elbow reaches opposite anterior axillary line = 1
  • Elbow at midline = 2
  • Elbow does not reach midline = 3
  • Elbow does not cross proximate axillary line = 4
Heel to Ear: With the infant supine, hold the infant’s foot with one hand and move it as near to the head as possible without forcing it. Keep the pelvis flat on the examining surface. Score as shown in the diagram above.

Physical Maturity

Sticky, friable, transparent
Gelatinous red, translucent
Smooth pink, visible veins
Superficial peeling and/or rash, few veins
Cracking, pale areas, rare veins
Parchment, deep cracking, no vessels
Leathery, cracked, wrinkled
Bald areas
Mostly bald
Plantar Creases
Heel-toe 40-50 mm = -1,
Heel-toe >50 mm, no creases
Faint red marks
Anterior transverse crease only
Creases over anterior 2/3
Creases over entire sole
Barely perceptible
Flat areola, no bud
Stippled areola, 1-2 mm bud
Raised areola, 3-4 mm bud
Full areola, 5-10 mm bud
Eye & Ear
Lids fused, loosely = -1, tightly = -2
Lids open, pinna flat, stays folded
Slightly curved pinna, soft with slow recoil
Well-curved pinna, soft but ready recoil
Formed and firm, with instant recoil
Thick cartilage, ear stiff
Genitals, male
Scrotum flat, smooth
Scrotum empty, faint rugae
Testes in upper canal, rare rugae
Testes descending, few rugae
Testes down, good rugae
Testes pendulous, deep rugae
Genitals, female
Clitoris prominent, labia flat
Prominent clitoris, small labia minora
Prominent clitoris, enlarging minora
Majora and minora equally prominent
Majora large, minora small
Majora cover clitoris and minora

Maturity Rating

Add up the individual Neuromuscular and Physical Maturity scores for the twelve categories, then obtain the estimated gestational age from the table below.
Total Score
Gestational Age, Weeks
Total Score
Gestational Age, Weeks


“New Ballard Score, expanded to include extremely premature infants,” by Ballard, JL, et al, Journal of Pediatrics, September 1991, page 417.
“A simplified score for assessment of fetal maturation of newly born infants,” Journal of Pediatrics 95:769, 1979.
Klaus and Fanaroff, “Care of the High-Risk Neonate,” Third Edition, pages 80-83.

Scoring System for Clinical Assessment of Klimek’s maturation index in newborn infants.

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