Objective: To assess the effect of parity on endovascular trophoblastic invasion in early pregnancy.
Design: Observational study.
Setting: Teaching hospital.
Patient(s): Healthy women at 10-14 weeks of gestation.
Intervention(s): Surgical termination of pregnancy for nonmedical reasons.
Main outcome measure(s): Products of conception were blindly examined histologically with regard to the extent of decidual endovascular trophoblast invasion.
Result(s): Samples were obtained from 20 nulliparous and 10 parous women. The presence of normal intradecidual endovascular trophoblast invasion was identified with a similar frequency in both groups (P=.28). However, the proportion of decidual vessels with endovascular trophoblast invasion was significantly higher in parous women (60%) compared with nulliparous women (32%, P<.001).
Conclusion(s): Endovascular trophoblast invasion in early pregnancy is more extensive in parous women who already had an uncomplicated pregnancy than in nulliparous women.