A prior early delivery often raises concerns about the outcome of subsequent pregnancies. A birth is considered “early,” or preterm, if it occurs before 37 completed weeks of gestation. Having a history of preterm birth (PTB) is recognized as the single most significant risk factor for a recurrence in a future pregnancy. While this previous event increases the likelihood of delivering early again, medical science offers proactive management strategies to mitigate this risk.
Understanding the Statistical Recurrence Risk
The general population risk for a preterm birth is approximately 10% of all pregnancies. For a woman who has experienced one spontaneous preterm birth, the risk of having a second one rises significantly, typically ranging from 15% to 30%. This recurrence risk depends heavily on the gestational age of the first early delivery.
The earlier the first baby was born, the greater the likelihood of a repeat event. A previous delivery occurring at an extremely early gestational age, such as before 32 weeks, carries a much higher recurrence risk compared to a previous delivery that happened closer to 37 weeks. Furthermore, a history of two previous preterm births increases the probability significantly for the third pregnancy. This escalating pattern highlights the importance of a detailed obstetric history to estimate the personal risk profile for the next pregnancy.
Modifying Factors That Increase or Decrease Risk
The statistical risk for recurrence is not fixed and can be influenced by several physiological and behavioral factors. One of the most important factors is the time between pregnancies, known as the interpregnancy interval (IPI). A short IPI, defined as less than 12 months between delivery and the next conception, is associated with a higher risk of recurrent preterm birth. Conversely, allowing for a longer interval, ideally 18 to 48 months, helps the body recover and contributes to a lower risk.
The reason for the previous early delivery also modifies the subsequent risk. A spontaneous preterm birth (sPTB), resulting from preterm labor or premature rupture of membranes, is the type most strongly linked to recurrence. A medically indicated preterm birth (iPTB), where delivery is induced due to maternal or fetal complications like severe preeclampsia, carries a high risk of repeating the same complication. Chronic conditions such as pre-pregnancy diabetes, chronic hypertension, and certain autoimmune disorders increase the chance of early delivery, particularly iPTB.
Lifestyle and physical health factors also modify the risk of recurrence. Behavioral factors like smoking and substance use are consistently associated with an increased risk for preterm birth. Certain infections, including urinary tract and reproductive tract infections, can trigger the inflammatory cascade that leads to spontaneous preterm labor. Addressing these modifiable factors before and during pregnancy can help reduce the overall chance of a recurrence.
Preventative Medical Strategies for Subsequent Pregnancies
For women with a history of spontaneous preterm birth, proactive medical management is a standard part of subsequent prenatal care. The first-line preventative strategy is often progesterone supplementation. This hormone is typically administered as weekly intramuscular injections or as a daily vaginal gel or suppository. Progesterone therapy is offered to women with a singleton pregnancy and a history of prior sPTB, and it has been shown to significantly reduce the risk of recurrence.
Another approach involves close monitoring of the cervical length via transvaginal ultrasound, usually starting in the second trimester. A finding of a short cervix, typically defined as less than 25 millimeters, identifies a subgroup at very high risk for a spontaneous preterm delivery.
For women found to have a short cervix, especially those with a prior sPTB, treatment may involve the use of vaginal progesterone or a surgical procedure called a cervical cerclage. A cerclage involves placing a suture around the cervix to provide mechanical support. It is most commonly used for women with a history of second-trimester loss due to cervical insufficiency or for those identified with a very short cervix on ultrasound. Both vaginal progesterone and cerclage are effective interventions for preventing preterm delivery in this high-risk group. Comprehensive care, including early consultation with a maternal-fetal medicine specialist and consistent prenatal visits, is foundational to implementing these preventative strategies.