From the Guidelines
A normal uterine lining thickness postpartum is typically considered to be less than 8-13 mm, with the exact thickness varying based on the time postpartum and individual factors. The uterine lining thickness postpartum gradually decreases over time as the uterus involutes, with the endometrium typically being 15-20mm thick immediately after delivery, decreasing to approximately 10-15mm by 2 weeks postpartum, and returning to pre-pregnancy measurements of 3-8mm by 6-8 weeks postpartum 1. This progressive thinning occurs as part of normal uterine healing, where the placental site undergoes repair and the decidual layer is shed.
- Key factors influencing uterine lining thickness postpartum include:
- Time postpartum: with the thickness decreasing over time
- Breastfeeding status: as prolactin levels can delay the return of normal menstrual cycles and affect endometrial thickness
- Presence of complications: such as retained products of conception or endometritis, which can cause a thickened endometrial echo complex with a variable cutoff of 8 to 13 mm 1
- It is essential to note that a thickened endometrium beyond the expected timeframes may indicate retained products of conception or other pathology requiring medical evaluation, and ultrasound can be used to assess for coexisting pathology and complications, such as RPOC, hematoma, or abscess 1.
From the Research
Normal Uterine Lining Thickness Postpartum
The normal uterine lining thickness postpartum can vary depending on several factors, including the method of delivery and the individual's parity.
- Studies have shown that the endometrial cavity measurement can range from 1.1 to 1.15 cm in the postpartum period, with no significant difference between vaginal and cesarean deliveries 2, 3.
- The presence of echogenic material in the endometrial cavity is a common finding in the postpartum period, particularly after vaginal delivery, and is not associated with bleeding complications 2, 3.
- Uterine involution, including the reduction in uterine size and endometrial thickness, is a gradual process that occurs over several weeks postpartum 4, 5.
- Breastfeeding has been shown to influence uterine involution, with women who breastfeed having a shorter uterine length and width at 3 months postpartum compared to those who do not breastfeed 5.
Factors Influencing Uterine Lining Thickness
Several factors can influence uterine lining thickness postpartum, including:
- Parity: Increasing maternal parity has been associated with larger uterine size at 1 month postpartum 5.
- Breastfeeding: Breastfeeding has been shown to influence uterine involution, with women who breastfeed having a shorter uterine length and width at 3 months postpartum compared to those who do not breastfeed 5.
- Method of delivery: Cesarean section has been associated with a larger uterine size at 1 and 3 months postpartum compared to vaginal delivery 5.
Ultrasound Evaluation
Ultrasound evaluation of the postpartum uterus can provide valuable information on uterine size, endometrial thickness, and the presence of echogenic material in the endometrial cavity.
- Transabdominal ultrasound is suitable for examination of the uterus during the first 14 days postpartum, while transvaginal ultrasound is preferable from day 28 onwards 4.
- Ultrasound measurements of the endometrial cavity and uterine size can help identify normal and abnormal findings in the postpartum period 2, 3.