Sporadic and Recurrent Miscarriages
Miscarriage is the spontaneous loss of a pregnancy before the baby becomes viable. The baby is usually considered to be viable from 23 completed weeks. Sporadic miscarriage is the commonest complication of pregnancy and is ‘random’. Current estimates suggest that only 50% of pregnancies progress to the stage where they are recognised by the pregnant woman and/or her doctor. Still, one in 6 recognised pregnancies will end in a miscarriage. We now know that many miscarriages occur even before women miss their period. The commonest cause of a single miscarriage is a random genetic abnormality in the embryo and the frequency of occurrence increases with increasing maternal age. Miscarriage can be ‘early’, that is, occurring before 13 completed weeks, or ‘late’, occurring between 14 and 23 weeks. Late miscarriage is closely related to, and shares common risk factors with preterm birth and rupture of fetal membranes. The commonest risk factors involved in this subset of miscarriage include infections and disturbances of the bacterial groups that live in the vagina such as bacterial vaginosis, aerobic vaginitis and group B streptococcus.
Recurrent miscarriage is conventionally defined as the loss of three or more consecutive pregnancies. Recurrent miscarriage is much less common than sporadic miscarriage and affects about one in 100 women. Immunological factors, hormone imbalance, and parental chromosomal disorders may be involved but majority of women who miscarry three or more pregnancies actually miscarry genetically normal babies and would therefore benefit from investigation. Furthermore, miscarriage is uncommon (less than 2%) amongst pregnancies that reach, and are viable at 8 weeks, even in the presence of bleeding. It is therefore reasonable to investigate miscarriages that occur at 8 weeks or beyond if the baby was viable up to that stage. Other women who may benefit from earlier investigation are those who have had two consecutive miscarriages with no children, as they are more likely to miscarry again compared to their peers who have had only one, or no miscarriage.
Generally we do not recommendation investigation if you have had a single first trimester pregnancy loss before 8 weeks. Where appropriate, we offer screening for infections, immunological disorders, chromosomal abnormalities and blood disorders.