Spontaneous miscarriage can be a very distressing and unfortunately common occurrence. It is thought that approximately one in three pregnancies end up in a miscarriage, and around two thirds of which occur before the pregnancy is even clinically evident.
There are many risk factors associated with increased chances of miscarriage. The most well documented factors include increasing maternal age, previous miscarriages and smoking. The most important of these is maternal age, ranging from a miscarriage rate of 15 percent in women aged under 30, to 20 percent at 35 years of age, to 40% at age 40 and 80% at age 45. Other risk factors are chromosomally or structurally abnormal pregnancy, maternal chronic disease or thrombophilias or uterine anomalies such as septum, fibroids or intrauterine adhesions, or cervical anomalies.
Risk factors that have less consistent evidence include very high caffeine intake, high alcohol intake, maternal obesity and fever. There is also a suggestion of increase risk of miscarriages with male factors such as advancing paternal age and/or abnormal semen parameters.
Advancing gestation after the first trimester, in a chromosomally and structurally normal pregnancy, is associated with a dramatically decreased miscarriage risk (less than 1%). Women who have previously had a child are also less likely to miscarry than the general population (5% overall risk). However, it is noted that these statistics may vary depending on other factors including maternal age.
It is important to acknowledge that it may be normal for some women and couples to go through grief reactions of differing severity. More often than not, a cause of the miscarriage will not be certain or diagnosable. Some women may need reassurance after a miscarriage that they did not cause the miscarriage by anything they have done, such as sexual intercourse, heavy lifting, bump to the abdomen or stress.
The general advice is to wait two to three months after a miscarriage before trying again to conceive. However, evidence for this is not substantial. There has been more recent data to suggest no greater risks of adverse outcomes if subsequent pregnancy occurs sooner than three months after a miscarriage. A recent study involving more than 600 subjects published in 2014 showed that there were similar live birth, miscarriage, and other pregnancy complication rates if conception occurred sooner compared with later than three months. Therefore, it is more worthwhile to ensure these women feel emotionally and physically ready to conceive again before they recommence trying, no matter the interval of waiting.
After miscarriage, the predictive risk in future pregnancies of another miscarriage is around 14 percent after one miscarriage, and 26 percent after two miscarriages and 28 percent after three miscarriages.
Investigations for recurrent miscarriages are usually recommended after the third miscarriage, because mathematically the observed frequency of three consecutive miscarriages is slightly higher than expected from chance alone. However, this depends on the baseline risk of miscarriages and can differ between different population groups. Generally investigations for recurrent miscarriages may include genetic testing for both partners, testing for maternal endocrinological and thrombophilia conditions as well as more detailed investigations of the uterus looking for structural anomalies including hysteroscopy.
Miscarriages are unfortunately a very common occurrence. The causes and experiences after a miscarriage may vary for different women and couples. It can be a time of great stress and anxiety for some. Most women will benefit from a conversation with their doctor to discuss their concerns and plans before moving forward, no matter their situation.