Postterm infants: too big or too small?

Concern over the postterm pregnancy has shifted from that of the difficult delivery of an excessively large fetus to the current concern with death in utero of an undernourished, small-for-date fetus. Studies of postterm pregnancy before the availability of ultrasonography may have included a large proportion of erroneous menstrual dates. The present study of 7000 infants was undertaken to reassess fetal growth in postterm pregnancies in which the expected date of confinement from last normal menstrual period dating was confirmed (+/- 7 days) by early ultrasonography. Results show a gradual shift toward higher birth weight and greater crown-heel length and head circumference between 273 and 300 days of gestational age. No evidence of postterm weight loss or lower weight for length could be demonstrated. Concern in postterm pregnancy should be for fetal macrosomia, not for intrauterine growth retardation.