Secondary outcomes included those that have been previously associated with postterm pregnancies including: meconium, postpartum hemorrhage, and chorioamnionitis.

Neonatal outcomes of macrosomia (birthweight greater than or equal to 4,000 gms) and Apgar score less than 7 were also examined.

Again, this would decrease the perceived difference in perinatal complications between term and postterm pregnancies.

Of note, since it appears that women are more likely to be oligo-ovulatory than poly-ovulatory, the former situation is more likely to exist, thus more women may have been traditionally misdiagnosed as postterm.

Further, women with a first trimester ultrasound should demonstrate a greater difference in perinatal complications between those with term and postterm pregnancies than those with a second trimester ultrasound only.

In order to test the hypothesis that improved ultrasound dating by first trimester ultrasound both decreases the diagnosis of postterm pregnancy and increases the differential in perinatal complications in those with a postterm pregnancy, we examined this effect in a cohort of women at our institution.

In the setting of pregnancies that are actually earlier than predicted, when they progress beyond 41 or 42 weeks of gestation, they are actually earlier and carry the lower risks of an earlier gestation decreasing the difference in perinatal complications ().

In the setting of pregnancies that are actually further along than predicted, when they deliver at 37–39 weeks of gestation, but are actually 40–42 weeks of gestation, they would increase the perceived risk of term complications among the younger gestational age group.

This may, in turn, reduce unnecessary intervention and lead to better identification of postterm pregnancies at greater risk of complications.

This definition is based primarily on outcomes research more than two decades old that demonstrated that pregnancies progressing beyond 42 weeks gestation had higher rates of morbidity and mortality.

In the OBUS12 group, the rate of postterm pregnancy ≥42 weeks was lower (2.7%) as compared to the OBUS13–24 group (3.7%, p=0.022).