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| The Uterus in Early Pregnancy |
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Few topics in Obstetrics are as complex and misunderstood as Recurrent Pregnancy Loss (RPL). Few complications in Obstetrics are as emotionally devastating for struggling couples. Yet, RPL is very common. In fact, 1% of women have had more than one miscarriage. What are causes for multiple miscarriages? What can be done to improve future outcomes in women with multiple miscarriages?
Traditionally, recurrent miscarriage or RPL has been defined by 3 early miscarriages (before 20 weeks). More recently, studies have shown similar outcomes if only 2 pregnancies have been lost, and therefore if a couple has two, without a normal pregnancy, a full work-up is indicated. In addition, there are key differences when women lose pregnancies in the first trimester or the second trimester, so this distinction is also important. Timing of the recurrent miscarriages helps guide the work-up of the patient as well. The following section is devoted to multiple miscarriage causes.
Early Recurrent Pregnancy Loss:
By far, the most common causes for early miscarriage are chromosomal abnormalities of the fetuses. Given how common this is in all conceptions, statistically many woman will simply have two, three or even four in a row. However, sometimes this can be a sign of abnormalities with the parent's chromosomes, that when passed in the wrong combination is lethal for the fetus. For instance, if a parent has a balanced translocation, or switch of parts of two chromosomes, that parent will still have a normal total number of chromosome material. If, however, they pass to their fetus just the chromosome that is too big, or too little, and not the right combination, the fetus will get unequal material. This may cause RPL or other birth defects. For this reason, detailed tests of the parents chromosomes is a vital part of determining miscarriage causes. There is no treatment to fix these types of translocations. If the fetus gets the right complement of genetic material then survival and normalcy is possible, even likely. However, there is no predicting how many pregnancies will be lost until this occurs. Alternatively, donated eggs/ sperm may be considered.
The uterine abnormalities are other common causes for early (and late, see below) RPL. The most common defect a woman is born with that causes RPL is a uterine septum, which is a wall within the uterine cavity. The causes of the miscarriage in this setting is an inability of the fetus to receive the proper support from the thin septum. If the conception tries to implant on this "internal wall" the fetus will be unable to be supported and will not survive early pregnancy. This type of anomaly can be diagnosed nonpregnant with a camera insertion into the uterus (hysteroscopy). It is also quite treatable, as the septum can simply be remove before the next conception. In addition, women who have had many d & c's or pelvic infections may have scarring of the lining of their uterus that prohibits growth of the fetus. Unfortunately, this is not treatable and successful pregnancy rates in these patients is quite low.
Hormonal reasons for loss are also described. The reasons for recurrent pregnancy loss in this setting are not as well-understood. Maternal Type I and Type II Diabetes is known to be one of the causes of miscarriage. This makes a mom with diabetes much more likely to have multiple miscarriages. Similarly, other hormone disorders, most commonly thyroid disorders, are also believed to have rates of miscarriage. Optimal control of these disorders prior to conception improves the success rate for the pregnancy.
A particular defect in the production of progesterone, or corpus luteal deficiency, has also been described. The true existence of this disorder is controversial. Progesterone supports the pregnancy. In corpus luteal defects, a woman does not produce normal amounts of progesterone with places the pregnancy at risk for loss. Progesterone supplementation can improve future pregnancy outcomes.
There are also disorders of the immune system which probably contribute to recurrent miscarriage though this is not well-understood. It is quite a miracle that a fetus first dives into the bloody cushion of the endometrium. It then sets up a host of villi that penetrated into maternal tissue, makes a placenta, bag of water, and baby. It stays there for nine months, grows, exchanges nutrients, oxygen, water, even antibodies with the mom. Never thought of your baby as the perfect little parasite before, did you? But, it is. Somehow, the mother does not recognize this foreign body, as it would an infection. How does that work? I wish I knew too! What a miracle! Some women with RPL loss, however, seem to reject their partners proteins that coat the fetus, and they do treat the pregnancy like an infection. This can cause both early loss and later stillbirth (see antiphospholipid antibody syndrome below).
Infection, stress, other maternal medical conditions, possibly large amounts of caffeine intake, paternal alcoholism and smoking have also been implicated as reasons for miscarriage that are recurrent.
Second and Third Trimester Pregnancy Loss:
Less commonly, women may experience RPL of pregnancy. Though there is some overlap, there are also unique reasons for recurrent late pregnancy losses. Chromosome problems should still be considered, however these are less likely to cause late recurrent pregnancy loss.
A weak cervix, or cervical incompetence, is known to cause RPL. Usually, the loss occurs between 18 and 26 weeks. Some women are born with a weak cervix. A weak cervix may develop after surgeries on the cervix (usually for abnormal Pap smears). Multiple surgical terminations or d & c's can also damage the cervix. With cervical incompetence, the cervix passively dilates, usually without symptoms. This usually occurs over several weeks as the pregnancy puts increasing pressure on the cervix. If undiagnosed, this can lead to rapid and unexpected delivery of the fetus. For details about diagnosis and treatment, see the page I have devoted to this topic, link below.
Other uterine birth defects are associated with recurrent pregnancy loss. Some women have a heart-shaped uterus, or bicorneate uterus. Others have a uterus completely divided in two, or uterine didelphys. These defects of the uterus may render it incapable of expanding properly to hold a growing pregnancy. Surgical correction of these anomalies may be considered, and may improve outcomes in future pregnancies.
Some maternal medical illnesses can cause late RPL. Severe blood pressure, kidney, cardiac, and blood clotting disorders, or thrombophilias, are the most common culprits. Severe chronic hypertension puts a woman at very high risk for early and severe preeclampsia, see link below. Several blood clotting disorders, thrombophilia's or "clot-loving" disorders can also cause late RPL. In particular, women with antiphospholipid syndrome, like lupus anticoagulant and anticardiolipin antibody syndromes, may have recurrent, late pregnancy loss. Simple blood tests can diagnose these disorders. When the placentas of these pregnancies are closely examined, it appears as though they have been showered with small clots for the duration of the pregnancy. Blood thinners may improve future pregnancy outcomes in these women, though this is actively being studied currently. In addition, women with antiphospholipid antibodies should be watched very closely for the development of leg clots and lung clots, which can be fatal. The highest risk time for these complications is in the postpartum period.
Unfortunately, many if not most women with recurrent pregnancy loss will never receive a formal diagnosis of what has caused their losses. The good news is that even in these couples, almost 50% will go on to have a successful future pregnancy.
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