What Is Amniocentesis?
Amniocentesis is the most common and one of the oldest invasive procedures in prenatal medicine. The amniocentesis procedure involves the aspiration of fluid from the womb of the pregnant mother. This fluid-filled inside the womb is called amniotic fluid which provides a cushioning effect and nutrients to the baby. Amniocentesis is helpful in diagnosing or excluding fetal genetic, biochemical, or infectious risks. The doctor will perform amniocentesis after 16 weeks of gestation.
Can Amniocentesis Cause Miscarriage?
The actual risk of miscarriage accounted for the amniocentesis procedure is yet not clear. The initial evaluation of amniocentesis-related miscarriage rate during the 1970s was 0.3 to 1.5 percent. In the 1980s, a prospective randomized trial study showed a risk of 1 percent. In the 1990s two meta-analysis studies showed a risk of 0.6 percent, whereas the latest study in 2020, found the miscarriage rate below 0.5 percent. This diverse result for miscarriage is because of the lack of data from randomized trials and due to the variety of the study method and populations involved. However, studies also showed that the risk of a miscarriage increases with multiple attempts of amniocentesis, due to the presence of blood-stained amniotic fluid. The risk of procedure-related miscarriage can be reduced with experience and familiarity with the amniocentesis procedure by the performing doctor.
However, there are some cases of miscarriage that occur after amniocentesis. But they are not associated with only the amniocentesis procedure alone, in fact, the fetal loss rate is also found to be associated with the mother’s age at the time of pregnancy and other underlying risk factors including pathological conditions of mother and baby as well.
What Are the Other Risk Factors That Increase the Risk of Miscarriage After Amniocentesis?
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The Mental Health of Pregnant Women: Mental health during the peripartum period is highly important for women and the developing baby in the womb, as anxiety, stress, and depression during pregnancy are related to alterations in fetal and infant neurobehavioural development. Moreover, mental conditions are also a risk factor for the development of postpartum depression as well. In addition, women struggling with infertility may have higher levels of general anxiety and mental stress than women who have conceived naturally, during the time of the first pregnancy. As amniocentesis is prenatal invasive testing further increases maternal anxiety. With this invasive procedure, some consequent issues such as cramping, pain, and vaginal spotting may occur after the procedure. Moreover, in some cases, minimal amniotic fluid leakage also can occur. These complications of the procedure may exaggerate the mental condition of the mother, which puts her at risk of miscarriage.
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Leakage of Amniotic Fluid: Women who experience leaking of amniotic fluid after amniocentesis as it is the procedure that involves puncturing the amniotic sac and retrieving amniotic fluid for the test. This leakage may occur in some women which further increases the risk of infection, fetal compromise may also happen due to compression of the cord that supplies the baby, premature rupture of membranes may also occur, and risk of preterm delivery.
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Fetal Abnormalities: A positive screening test during the first or second trimester suggests fetal genetic abnormalities. These fetal chromosomal abnormalities are also one factor in the risk of miscarriage after amniocentesis.
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Mother’s Age at the Time of Pregnancy: The risk of a miscarriage increases steeply after a women’s age of 35 years. It rises from 9 percent at 20 to 24 years to 75 percent after 45 years of age.
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Past History of Miscarriage: Another important predictive and risk factor for fetal loss outcome is reproductive history. Research among women after an amniocentesis procedure established that women in their first pregnancy and women with a history of live baby births have a low risk of miscarriage during their next pregnancies compared to women who had a fetal loss in their most recent pregnancy. According to a study report, women with a history of more than three miscarriages or induced abortions have four times more risk of miscarriage than other women after undergoing amniocentesis.
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Bleeding: Bleeding is also a risk factor for pregnancy loss associated with amniocentesis. Even without an invasive procedure, a history of spotting and serious bleeding in the first and early second trimesters are independent risk factors for a miscarriage. For the amniocentesis procedure, bleeding two weeks before the amniocentesis procedure is a contraindication. Studies data suggest that invasive diagnostic procedures like amniocentesis in case of previous bleeding may lead to miscarriage.
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Blood-Stained Amniotic Fluid: Miscarriage is also related to intra-amniotic bleeding. Blood in amniotic fluid even without a history of vaginal bleeding may cause fetal loss. When amniotic fluid is blood stained at amniocentesis, it indicates an old intra-amniotic hemorrhage. In such cases, the risk of a miscarriage is almost six times higher. On the contrary, amniotic fluid mixed with fresh blood such as in cases of placenta perforation, the risk of miscarriage is not higher than in clear amniotic fluid cases. Thus, miscarriage after retrieval of blood-stained amniotic fluid is a result of hemorrhage.
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Uterine Fibroids: The presence of fibroids in the uterus is also an independent predictive risk factor for miscarriage. Women who had uterine fibroids more than 20 mm in size have almost three times higher risk of miscarriage after amniocentesis. Women who had undergone surgery to remove the fibroids did not have an increased risk for fetal loss. This is true for any uterine surgery history.
Conclusion
Amniocentesis is the most commonly performed invasive procedure for prenatal genetic testing. However, amniocentesis is a relatively safe procedure and has fewer complications including miscarriage in rare cases. The actual miscarriage risk of an amniocentesis procedure is still uncertain and is certainly multifactorial. Gynecologists usually advise pregnant women to undergo amniocentesis for any reason such as an abnormal screening test or major ultrasonographic markers for fetal abnormalities. In that case, a woman should not be worried about the risk and should consult and communicate better regarding solving any doubt regarding the risks in her case. The genetic counselor can also be extremely helpful, to understand the risks of the testing procedures and also will guide the couple in case of any possibility of abnormal results.
