Miscarriage is a common consequence of pregnancy. In most cases, 12-15% of miscarriages occur within 20 weeks of conception. However, determining the total miscarriage rate in one country is very challenging because it is higher when the pregnancies are medically recognised. Moreover, there is an unclear conception among people about the difference between miscarriage and stillbirth. The miscarriage rate is also affected by the competing risk of induced abortion.
The causes of most miscarriages are a complex interplay between parental age, genetic, hormonal, immunological, and environmental factors. Maternal age is the strongest known risk factor. The risk of miscarriage is slightly elevated in the youngest mothers and then rises sharply in older mothers.
A survey of 421,201 pregnant women in Norway between 2009-13 suggests that the risk of miscarriage is lower in women aged 25-29 (10%), then rose rapidly after age 30, reaching 53% in women aged 45 and over. Genetic factors, including parental chromosomal rearrangements and abnormal embryonic genotypes or karyotypes, could underlie more than half of recurrent miscarriages. Miscarriage may adversely affect future pregnancy outcomes and complications.
About 75% of miscarriages happen during the first trimester of pregnancy; infection around the baby and its mother's health condition affect greatly in this stage. In this trimester, miscarriages are often caused by problems with the chromosomes of the foetus. The mother's placenta supplies blood to her baby's body; any problem in this organ may lead to miscarriage. Moreover, obesity, smoking, drinking alcohol, certain drugs (e.g., misoprostol, retinoids, methotrexate, ibuprofen) and caffeine at high dose (200 mg/kg/day), also increase the risk of miscarriage among pregnant women.
Several long-term (chronic) health conditions also increase the risk of miscarriage in the second trimester, including diabetes (if left uncontrolled or poorly-controlled), severe hypertension, lupus, kidney disease, thyroid gland's under or overactivity, anti-phospholipid syndrome, problems and abnormalities in the womb (e.g., fibroids and shape abnormality), weakened cervix or cervical incompetence, and polycystic ovary syndrome (also causes infertility).
Many infections may increase the risk of miscarriage, such as rubella (German measles), cytomegalovirus, bacterial vaginosis, human immunodeficiency viruses, chlamydia, gonorrhoea, syphilis, malaria, etc. The severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) induced placental infection also has been reported for newborns with foetal distress and stillbirth after the maternal contraction of the virus during the third trimester.
However, there are lots of misconceptions about miscarriage, including the emotional state of the woman, having a shock or fright, exercise, lifting or straining, working, having sex, travelling by air and eating spicy food during pregnancy; as these are not the risk factors in miscarriage (if no one crosses the limit).
Many women having a miscarriage for the first time may have another. But most miscarriages are a one-off event. About 0.01% of women experience recurrent miscarriages and many of them go on to have a successful pregnancy.
The writer is an Assistant Professor of Pharmacy at the Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj, Bangladesh.