Possible Causes of Recurrent Miscarriages

I have had two miscarriages in the first ten weeks of pregnancy. What are some of the possible causes?

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Spontaneous abortion, commonly called a miscarriage, is the most common complication associated with pregnancy. It has been estimated that approximately two-thirds of human conceptions (fertilized oocyte) fail to achieve viability and an estimated 50 percent are lost before the first missed menstrual period.

Approximately 12 to 15 percent of clinically recognized pregnancies (a gestational sac in the uterus) are lost within the first 12 weeks of pregnancy (first trimester loss).

Chromosomal abnormalities are responsible for approximately 50 percent of first trimester pregnancy losses. Of the chromosomal abnormalities, the majority are autosomal trisomies (22.3 percent), followed by monosomy X (8.6 percent), triploidy (7.7 percent) and tetraploidy (2.6 percent). Go to http://www.ncbi.nlm.nih.gov/PubMed/ to learn more, and use the search words "first trimester pregnancy loss" and "chromosomal abnormality."

The chances for a viable birth after one miscarriage are approximately 76 percent. After two and three miscarriages, the chances for a live birth are 70 and 65 percent, respectively. When one has experienced four miscarriages, a live birth can be anticipated in approximately 60 percent of these pregnancies.

Recurrent abortion or recurrent miscarriage has been defined as the occurrence of three or more clinically recognized pregnancy losses before 20 weeks from the last menstrual period.

An excellent link that explores a variety of potential causes of recurrent miscarriages can be found at http://www.ncbi.nlm.nih.gov/PubMed/. After each condition, I have included the search terms that you can use to access specific information on the site.

Causes of recurrent miscarriages:

  • Genetic abnormalities
  • Endocrine disorders (search terms: "first trimester pregnancy loss" and "luteal phase defect").
  • Thyroid disorders (search terms: "first trimester pregnancy loss" and "thyroid disorders").
  • Diabetes mellitus (search terms: "first trimester pregnancy loss" and "diabetes mellitus").
  • Hyperprolactinemia (search terms: "first trimester pregnancyloss" and "hyperprolactinemia").
  • Acquired anatomic abnormalities (search terms: "first trimester pregnancy loss" and "leiomyomas").
  • Endometriosis (search terms: "first trimester pregnancy loss" and "endometriosis").
  • Uterine synechiae (search terms: "first trimester pregnancy loss" and "uterine synechiae").
  • Cervical incompetence (search terms: "first trimester pregnancy loss" and "cervical incompetence").
  • Congenital anatomic abnormalities (search terms: "first trimester pregnancy loss" and "Mullerian duct").
  • Iimmunologic factors (search terms: "first trimester pregnancy loss" and "antiphospholipid").
  • Infections (search terms: "first trimester pregnancy loss" and "infection").

Evaluation for these abnormalities usually begins after two or three miscarriages. Most physicians recommend waiting two complete cycles prior to reattempting pregnancy because of the high incidence of endometrial abnormalities in the first two cycles after a miscarriage.

Avoiding pregnancy over the two subsequent cycles following a miscarriage will reduce the possibility of exposing a conception to an endometrial lining, which may not be capable of sustaining a pregnancy. Rhogam should be administered to a woman who is Rh negative. Grief is to be expected and occasionally counseling may be necessary.

In the case of recurrent miscarriage with a recognized and treated cause (anatomic, endocrine, infectious, antiphospholipid syndrome), one can anticipate a successful outcome in 70 to 90 percent of cases. In the case of genetic abnormalities, live births can be anticipated in 20 to 80 percent of cases depending on the genetic condition and the inheritance patterns. When no diagnosis can be made, general supportive care of the early conception yields 40 to 90 percent live birth rates.

When cardiac activity is seen at six weeks of gestation by ultrasound over 75 percent of these pregnancies will result in a live birth.

Some physicians initiate the workup for recurrent miscarriage after two losses, particularly if there has been cardiac activity initially.

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