Curriculum · Gynecology / Women's Health / Infertility / Perinatal Care / Birth Spacing
Miscarriage
What it is
Spontaneous miscarriage is loss of the pregnancy at less than 20 weeks of gestation. Death at 20 weeks or more, before or during birth, is stillbirth instead. Miscarriage is the commonest cause of bleeding in the first trimester, 15-20% of pregnancies (10-15% in the book), and its pain is midline; ectopic pregnancy causes 2% but is the commoner cause of death and its pain is lateral. The differential of bleeding in early pregnancy is miscarriage, ectopic pregnancy, molar pregnancy, and local causes such as a cervical polyp, cervical infection or vaginitis. Recurrent miscarriage is 3 or more miscarriages before 20 weeks of gestation. Bleeding is also divided by trimester. In the first it is spontaneous abortion, ectopic pregnancy and hydatidiform mole; in the second, spontaneous abortion, hydatidiform mole and placental abruption; in the third, bloody show, placental abruption, placenta praevia and vasa praevia. Alongside the pregnancy related causes, sexually transmitted infections and cervical polyps should be excluded.
Causes and risk
The most common cause of spontaneous abortion is a chromosomal abnormality or genetic factor, and the most common chromosomal abnormality is autosomal trisomy. Trisomies 13, 16, 18, 21 and 22 are the most common, and the most common specific anomaly is monosomy X (20%), then trisomy 16 (16%). First trimester risk factors are previous miscarriage; maternal health conditions (advanced maternal age, chronic DM, thyroid disease, SLE, antiphospholipid syndrome); and maternal infections (TORCH, CMV, rubella, HSV, bacterial vaginosis). Inadequate estrogen or progesterone deficiency is not a cause. Mid-trimester abortion (12-24 weeks) comes from fetal chromosomal disorders, uterine abnormalities (septate, bicornuate, fibroid, Asherman syndrome), placental abruption, placenta previa, cervical incompetence, multiple gestation, low progesterone or estrogen, smoking and alcohol. For recurrent miscarriage add age 35 years or more, obesity, smoking, alcohol and caffeine. The most common cause of first trimester recurrent abortion is a balanced translocation of chromosomes; the most common cause of second trimester recurrent abortion, and overall, is cervical incompetence. Infections do not lead to recurrent abortions, only to spontaneous pregnancy loss. The causes of recurrent miscarriage are grouped: idiopathic; anatomic, that is septate and bicornuate uterus, cervical incompetence, synechia, leiomyomas, adenomyosis and chronic endometritis; autoimmune, that is antiphospholipid syndrome, whose miscarriage is in the second trimester, and SLE; parental chromosomal abnormality, that is a balanced reciprocal translocation; and endocrine, that is DM, thyroid disease, hyperprolactinemia and PCOS. Antiphospholipid syndrome is diagnosed on one clinical and one lab criterion: clinically one or more thrombosis events, or three or more consecutive spontaneous pregnancy losses under 10 weeks, or one or more fetal deaths over 10 weeks, or preterm birth at GA<34 wks secondary to severe preeclampsia or placental insufficiency; and in the labs anticardiolipin, lupus anticoagulant or anti beta 2 glycoprotein, positive on two or more occasions three or more months apart. Its treatment is low dose aspirin with LMWH.