Causes of Postterm Pregnancy
Aug 24, 2022
Source: Cainiu Health
Dr. Lv Aiming
Introduction
Estimated due date (EDD) assessment is inaccurate. For pregnant women with regular menstrual cycles and normal ovulation, the EDD is generally accurate. Pregnancy lasting two weeks beyond the EDD is termed “post-term pregnancy.” Common causes include fetal macrosomia—particularly an oversized fetal head—which impedes fetal descent. A narrow pelvis (pelvic stenosis) may also hinder descent of the fetal head and contribute to post-term pregnancy. Pregnancy that reaches or exceeds 42 weeks’ gestation is defined as post-term pregnancy.
Early and late prenatal care is critically important for pregnant women—especially after the estimated due date—to avoid causing psychological stress related to concerns about fetal development. So, what causes post-term pregnancy?
Causes of Post-Term Pregnancy
Inaccurate estimation of the due date is a common cause. For women with regular menstrual cycles and normal ovulation, the estimated due date is generally reliable. Pregnancy is considered post-term if it extends beyond the due date by two weeks. Common contributing factors include fetal macrosomia—particularly an oversized fetal head—which impedes fetal descent into the birth canal. A narrow or contracted pelvis may also hinder descent of the fetal head, potentially leading to post-term pregnancy. Additionally, deficiencies in placental sulfatase, endogenous prostaglandins, and estrogen can result in inadequate uterine contractions, thereby delaying labor onset.
Pregnancy lasting 42 weeks or longer is defined as post-term pregnancy. Its incidence accounts for 5%–12% of all pregnancies. Perinatal morbidity and mortality rates increase significantly in post-term pregnancies—and rise progressively with increasing gestational duration. At 43 weeks’ gestation, the perinatal mortality rate is three times higher than that of term pregnancies; at 44 weeks, it is five times higher. Primiparous women face greater fetal risks from post-term pregnancy compared with multiparous women. Adverse effects on both fetus and mother include fetal distress, oligohydramnios (reduced amniotic fluid volume), dystocia (difficult labor), and birth-related trauma.
Post-term pregnancy warrants close clinical attention. Enhanced monitoring of both fetal well-being and maternal status is essential. If spontaneous vaginal delivery does not occur within a reasonable timeframe, cesarean delivery should be considered. We hope this information has been helpful to you!
