How Many Weeks Is a Pregnancy Considered Post-Term?

What does the evidence say about post-term pregnancy and induction timing during pregnancy?

1. ACOG defines late term as 41 weeks 0 days through 41 weeks 6 days and post-term as 42 weeks 0 days or later, and says induction may be recommended when pregnancy reaches 41 weeks. 1
2. For an otherwise uncomplicated pregnancy, ACOG surveillance guidance recommends testing from 41 weeks 0 days once or twice weekly until 42 weeks 0 days, when delivery is indicated. This is an individualized care plan, and reassuring monitoring cannot remove every risk between tests. 2
3. An individual-participant meta-analysis of randomized trials found severe adverse perinatal outcomes in 0.4 percent with induction at 41 weeks versus 1.0 percent with waiting until 42 weeks, without a higher cesarean rate. 3
4. The 1,801-participant INDEX randomized trial found adverse perinatal outcomes in 1.7 percent after 41-week induction and 3.1 percent with waiting until 42 weeks, while cesarean rates were 10.8 percent in both groups. 4
5. A Cochrane review found membrane sweeping may increase spontaneous labor and reduce formal induction, but evidence certainty was generally low and the optimal timing and frequency remain unresolved. 5

Is post-term pregnancy and induction timing safe in each trimester?

• First trimester. Accurate first-trimester dating matters because a due date based on a reliable early ultrasound reduces the chance that a pregnancy is mislabeled late term or post-term later.
• Second trimester. During the second trimester, review the established estimated due date before changing it. Later ultrasound is less precise for dating and generally should not replace a well-supported early date.
• Third trimester. At 41 weeks, discuss induction versus monitored waiting until 42 weeks using absolute risks, prior birth history, cervical readiness, local capacity, and personal preferences. Post-term begins at 42 weeks 0 days.