Miscarriage, also known as spontaneous abortion, in the second trimester of pregnancy is not so common although there are some risk factors. The second trimester of pregnancy is considered to be from 12th to 20th week of fetal gestation. Majority of miscarriages happen within the first twelve weeks, sometimes in the beginning of pregnancy that a woman is not aware of the fact that she had conceived and lost her baby. Miscarriages that occur in the first or at the start of second trimester account between 15 and 20 percent of all pregnancies. Any miscarriage that occurs after twenty weeks of pregnancy is termed as stillbirth.
In some cases, miscarriage may happen in the first trimester but detected during screening at the beginning of the second trimester and that is considered as missed miscarriage. The most common cause for the second trimester miscarriage is chromosome problem that occurs in the fetus. Apart from that weak cervix is a frequent cause of loss of baby during the second trimester. Uterine defects or clotting disorders as wells as previous spontaneous abortion can all lead to miscarriage during the second trimester of pregnancy.
Weak cervix is soften and weaker than normal cervix and it may begin dilating and opening too early in the pregnancy. Some women are born with weak cervix while some may have it because of the surgical procedure on the cervix. This surgery may be performed because of abnormal pap smears that required biopsies, or multiple abortions or D&C procedures. Weak cervix may start to dilate without causing any symptoms and as the weight of a growing fetus puts pressure on it causing it to dilate more that can result in unexpected pregnancy loss. In women with increased risk for miscarriage due to weak cervix, a doctor may recommend cerclage which is a stitch in the cervix.
Miscarriage in the second trimester can also be caused by uterine defects. Uterine defects include bicorneate uterus or heart-shaped uterus and uterine didelphys characterized by the uterus divided in two. Uterine didelphys can lead to inability of the uterus to grow and expand as the pregnancy progresses. Uterine abnormalities can be surgically treated to prevent pregnancy loss.
Mother affected with some illnesses may not be able to carry a full term infant. These illnesses include kidney, heart, blood pressure and clotting disorders. High blood pressure in pregnancy may lead to preeclampsia which is a high blood pressure and presence of protein in the urine. Women with clotting disorders such as, antiphospholipd syndrome, lupus anticoagulant or anticardiolipin antibody syndrome are at high risk for recurrent miscarriages. These conditions may be treated with blood thinning medications.