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Natural Pregnancy Loss: Miscarriage & Stillbirth


Natural pregnancy loss can be divided into miscarriage (before the 20th week), foetal demise and stillbirth (after the 20th week). At least 15% of clinically recognisable pregnancies end in foetal loss.
Miscarriages, or spontaneous abortions, are, along with ectopic pregnancies , the most frequent type of losses to occur in the first trimester (week 1-13).


Up to 50% of all tissue from miscarriages demonstrate chromosomal abnormalities. Therefore, chromosomal abnormalities are the primary cause of miscarriages. These aberrations occur early in embryonic development and many times do not even manifest a foetus. Unless one or both parents are carrying an abnormal chromosome, the risks of recurrence for these early miscarriages is low.

Implantation can be interrupted by a deficiency or imbalance in the production of maternal hormones , most often progesterone from the ovary and thyroxin from the thyroid gland. Maternal bacterial, viral or viral-like infections have also been associated with first trimester pregnancy losses. Three in particular are mycoplasma , Chlamydia , and gonorrhoea.   

Mycoplasma can actually be a cause of recurrent spontaneous abortions while Chlamydia and gonorrhoea. can also infect the uterus and fallopian tubes and damage the very delicate lining of the tubes (called tubal endothelium ) and create a hostile environment for the transport of the fertilised egg promoting an increased risk for a tubal or ectopic pregnancy.

Other factors which have been implicated as causes of first trimester losses include auto immune disorders such as the Anti-phospholipid syndromes , substance abuse , multiple pregnancies and placental abnormalities such as gestational trophoblastic diseases, the most common being molar pregnancies.  


Treatments for imminent miscarriage or first trimester loss are unfortunately usually expectant. Attempts have been made to prescribe strict bed rest, administer hormonal supplements as well as other exogenous therapies. In circumstances where there is a viable pregnancy and significant vaginal bleeding, bed rest might be beneficial to reduce trauma in an already precarious pregnancy. Such is the case with the so called vanishing twin syndrome where conception resulted in a twin gestation but one twin aborts causing bleeding while the remaining twin is viable. Progesterone therapy is thought to be of value in circumstances where it is felt there might be a reduction in progesterone production from the ovary leading to poor embryonic development (inadequate luteal phase.) Aspirin, steroids such as prednisone and heparin have been used with some success in the treatment of immunological causes of pregnancy loss.


The second trimester begins at about 13 weeks and continues until the 27th week. What make this trimester unique is that it spans a time period where a pre-viable foetus. becomes a potentially viable neonate, albeit premature . In current practice, 1995, it is generally felt that a preterm birth prior to 24 weeks is unlikely to survive, although it is not impossible and without hope. The third trimester shares similar aetiologies to the mid or second trimester. 

Factors that may increase the risk of a stillbirth include:

The information in this page is presented in summarised form and has been taken from the following source(s):
1. Hygeia Foundation :

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Contact Last modified: Jun 25 2002