Second-trimester loss refers to pregnancy loss occurring between the 13th and 27th weeks of gestation. These events are less common than those in the first trimester, which account for the majority of miscarriages. Understanding the potential causes of a second-trimester loss can offer clarity.
Maternal Health and Anatomy
Conditions related to the pregnant individual’s health and anatomy can contribute to second-trimester loss. Cervical insufficiency, where the cervix opens prematurely and painlessly, can lead to early delivery. This can happen if the cervix is weakened or damaged, sometimes due to previous surgical procedures.
Structural issues within the uterus can also interfere with pregnancy progression. Abnormalities like fibroids (non-cancerous growths) or an unusually shaped uterus (e.g., a uterine septum) can prevent proper fetal development or lead to complications. These anatomical variations can disrupt the uterine environment necessary for continued pregnancy.
Chronic health conditions in the pregnant individual can elevate the risk of second-trimester loss. Poorly controlled diabetes, severe hypertension, kidney disease, or autoimmune disorders like lupus can affect the overall health of the pregnancy. These conditions can impact blood flow and nutrient delivery to the fetus, increasing the likelihood of complications.
Infections also pose a risk during the second trimester. Bacterial vaginosis, a common vaginal infection, can ascend into the uterus, leading to inflammation of the membranes surrounding the fetus (chorioamnionitis). Certain viral infections, such as cytomegalovirus or parvovirus, can directly affect the fetus and lead to loss. Blood clotting disorders (thrombophilias) can cause clots in blood vessels, potentially disrupting blood flow to the placenta and contributing to pregnancy loss.
Fetal Development Issues
Issues originating from the fetus can also result in second-trimester loss. Chromosomal abnormalities, where the fetus has an incorrect number or structure of chromosomes, are a frequent cause of pregnancy loss. Conditions like Trisomy 18 or Trisomy 13 often lead to non-viable pregnancies, meaning the fetus cannot survive outside the womb.
Major structural birth defects can also be incompatible with continued development. Severe heart defects or neurological conditions like anencephaly (where the brain and skull do not form completely) are examples of anomalies that can lead to second-trimester loss. These serious developmental problems are often detected during routine ultrasound examinations.
Genetic syndromes (inherited conditions) can manifest during fetal development and cause complications. These syndromes might result in severe growth restriction or other developmental issues that prevent fetal survival. Many of these severe fetal issues are random occurrences and are not typically preventable.
Placental Complications
The placenta plays a central role in sustaining pregnancy, acting as the primary connection between the pregnant individual and the fetus for nutrient and oxygen exchange. Problems with this organ can severely compromise fetal well-being. Placental insufficiency, characterized by poor blood flow from the pregnant individual to the placenta, can deprive the fetus of necessary resources for growth and survival.
Placental abruption occurs when the placenta prematurely detaches from the uterine wall before birth. This can cause significant bleeding and interrupt the fetal oxygen supply, leading to serious complications. Placenta previa, where the placenta covers the cervix, can also lead to severe bleeding later in pregnancy.
Issues with the umbilical cord, which transports blood between the fetus and placenta, can also be a factor. Umbilical cord accidents, such as severe knotting, compression, or vasa previa (where fetal blood vessels cross near the birth canal opening), can restrict blood flow and oxygen to the fetus. Any disruption to the placenta’s function directly impacts the fetus, often with severe consequences.
When a Cause Isn’t Identified
Despite comprehensive medical evaluations, a specific cause for a second-trimester loss cannot always be determined. This can be a source of frustration and emotional distress for individuals and families experiencing such a loss. Even when a clear cause remains elusive, healthcare professionals often provide guidance based on general risk factors or observations gathered during the evaluation. Approximately half of second-trimester losses may not have an identifiable reason, even after thorough testing.