Identifying the optimal gestational age with minimal complications for mother and baby has been a topic of long-standing interest.
Advances in technology and access to care over the past few decades have led to a remarkable evolution in determining gestational age and identifying optimal time for delivery. Identifying the optimal gestational age with minimal complications for mother and baby has been a topic of long-standing interest.
The American College of Obstetricians and Gynecologists has long recommended a minimum of 39 weeks unless a maternal or fetal complication exists to recommend earlier delivery, with specific guidance available for those optimally delivered in the late preterm and early-term periods. Tita et al determined that even in the time period identified as “term”
(> 37 weeks), there are risks to delivering before 39 weeks.1 This led to redefining epochs of gestational age, including that of “early term” to define the 37th and 38th weeks of gestation.2
Importantly, the advent of ultrasound, especially first-trimester ultrasound to optimize dating, has had major implications on gestational-age dating and, hence, timing of delivery. It was anticipated with the advent of ultrasound, especially in the first trimester, that postdates pregnancy would cease. Ultrasound has enabled further-nuanced timing of delivery, even within a 1- to 2-week time frame in the setting of maternal, fetal, or obstetrical conditions.3,4
By 2013, women had an average of 4 to 5 ultrasounds in pregnancy, with at least half receiving a targeted ultrasound. In addition, in 2013, the definitions of late preterm (34w0d-36w6d), early term (37w0d-38w6d), full term (39w0d-41w6d), late term (41w0d41w6d), and post term (> 42w0d) were clarified and cemented into the literature.5 Thus, by this time, the dating of pregnancy was more commonly by—or at least incorporating—ultrasound. As seen in Figure 1, this resulted in a greater percentage of full-term deliveries and fewer early-term and late-preterm deliveries in 2016.6 Furthermore, the number of late-term and postterm deliveries has continued to decline.6
Interestingly, with these changes and the improved dating utilizing ultrasound, the timing of delivery has increased the number of deliveries at 39 weeks of gestation (Figure 2),6 which is likely predominantly due—given that the greatest increase is after 2007—to enhanced use of ultrasound rather than new definitions of terminology or trials demonstrating improved outcomes with induction in specific populations at 39 weeks.7
With enhanced access to early ultrasound and optimized pregnancy dating, situations that benefit from early delivery will improve outcomes for providers, patients, and families. Although so many obstetric practices have stood the test of time, innovation on the foundation of obstetrics—identifying gestational age—has made a major impact on our field.