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 | Â | 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 |