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Table 3 Gestational age methods, accuracy and limitations

From: Born Too Soon: The global epidemiology of 15 million preterm births

Method Accuracy Details Availability/feasibility Limitations
Early ultrasound scan +/- 5 days if first trimester
+/- 7 days after first
trimester
Estimation of fetal crown-rump length +/- biparietal diameter/femur length between gestational age 6 - 18 weeks Ultrasound not always available in low-income settings and rarely done in first trimester May be less accurate if fetal malformation, or maternal obesity
Fundal Height ~ +/- 3 weeks Distance from symphysis pubis to fundus measured with a tape measure Feasible and low cost In some studies similar accuracy to LMP Potential use with other
variables to estimate GA when no other information available
Last menstrual period ~ +/- 14 days Women's recall of the date of the first day of her last menstrual period Most widely used Lower accuracy in settings with low literacy. Affected by variation in ovulation and also by breastfeeding. Digit preference
Birthweight as a surrogate of gestational age More sensitive/specific at lower gestational age e.g.
<1500 g most babies are preterm
  Birthweight measured for around half of the world's births Requires scales and skill. Digit preference
Newborn examination ~ +/- 13 days for Dubowitz, higher range for all others Validated scores using external
+/or neurological examination of the newborn
e.g. Parkin, Finnstrom, Ballard and Dubowitz scores
Mainly specialist use so far. More accurate with
neurological criteria which require considerable skill. Potential wider use for simpler scoring systems
Accuracy dependant on complexity of score and skill of examiner. Training and ongoing quality control required to maintain accuracy
Best obstetric estimate Around +/- 10 days (between ultrasound and newborn examination) Uses an algorithm to estimate gestational age based on best information available Commonly used in high-income settings Various algorithms in use, not standardized
  1. Adapted from Parker, Lawn and Stanton (unpublished Master's thesis)