Uterine subinvolution is a postpartum condition where the uterus does not return to its pre-pregnancy size and state at the expected rate after childbirth. It involves the uterus remaining larger and softer than it should be.
Normal Uterine Involution
Uterine involution is a key postpartum process. Immediately following the delivery of the placenta, the uterus begins to contract. This process is essential for compressing blood vessels at the placental attachment site and preventing excessive bleeding. These contractions help the uterus steadily decrease in size.
The fundus, the top of the uterus, is typically at the level of the belly button about an hour after birth. It then descends by approximately one centimeter per day, becoming positioned at the pubic bone around one week postpartum. By 10 to 14 days, the uterus should be back within the pelvic cavity, and the entire involution process, including the shedding of the uterine lining known as lochia, usually completes within six weeks.
Why Subinvolution Occurs
Several factors can impede the uterus’s ability to contract effectively and return to its non-pregnant state. A frequent cause is retained placental fragments or other products of conception, which interfere with muscle constriction, leading to an enlarged, less firm uterus.
Uterine infections, such as endometritis, also contribute significantly, as the inflammation prevents proper muscle contraction. An overdistended uterus from conditions like multiple pregnancies, excessive amniotic fluid (polyhydramnios), or a large baby can weaken uterine muscles, making involution more challenging. Other contributing factors include prolonged labor, a history of many previous pregnancies (grand multiparity), uterine fibroids, or a full bladder, which can hinder uterine contraction.
Recognizing and Diagnosing Subinvolution
Identifying uterine subinvolution involves observing specific signs and symptoms in the postpartum period. Common indicators include persistent, unusually heavy vaginal bleeding, with lochia continuing beyond its typical duration. The discharge might also have a foul odor if an infection is present.
Patients may also experience prolonged afterpains, lower abdominal fullness or discomfort, or a uterus that remains larger or higher than expected on palpation. Diagnosis involves a physical examination assessing uterine height and firmness. Ultrasound may identify underlying causes like retained placental tissue or blood clots.
Treatment and Prevention
Treatment addresses the underlying cause and promotes uterine contraction. If retained placental fragments are suspected, dilation and curettage (D&C) may remove the tissue. For infections, antibiotics are typically prescribed.
Medical treatments include uterotonic medications like oxytocin and methylergonovine, which stimulate uterine contractions to help the uterus firm up and return to normal size. Preventative measures include frequent breastfeeding, which releases oxytocin to encourage uterine contractions. Regular bladder emptying is also important, as a full bladder can hinder uterine contraction.