Fibroids and Fertility
Do all fibroids impact upon fertility?
The short answer is no. Fibroids are estimated to account for, or contribute to around 1-2% of infertility. Fibroids that distort the lining of the uterus (endometrium) affect fertility by means that are at present, incompletely understood. Possibilities include:
- The endometrial vascularity over the fibroid may be altered, reducing fertility and
- There may be differences in the biochemical milieu and contractility of the uterus at the site of the fibroid.
Importantly, the location of the fibroid and not it’s absolute size is the key factor in whether or not it may affect fertility. Even very small fibroids, when distorting the endometrial cavity, may impact on fertility whereas large fibroids on the outside of the uterus may not. The issue of fibroids within the uterine musculature (intramural) is more difficult. At present, it is thought that intramural fibroids, of 4cm or more do affect fertility, but removing these fibroids may not necessarily restore spontaneous fertility rates to normal. Note that this is different in the case of IVF.
I strongly suspect that although removing these fibroids results in a fertility gain, some of that gain is negated with resultant adhesions. Thus the onus is on the gynecologist to remove the fibroid, returning the uterus in as perfect a fashion as possible, restoring myometrial continuity, with little chance of infection, hematoma or subsequent adhesion formation. This requires a meticulous surgical technique and I believe anti-adhesive measures to play a role. Please see Laparoscopic Removal of Fibroids for further discussion.
Do all fibroids interfere with a pregnancy?
Once again, the answer is no. Everything depends on the site and size of the fibroid. Interestingly if in comparing groups of women with and without submucosal fibroids, once they are pregnant the miscarriage rate is similar.
Around 50 to 60% of fibroids increase in size during pregnancy. Most of this growth occurs during the first trimester, slowing in the second and third trimesters. Large fibroids greater than 5cm are more likely to grow where as smaller fibroids may remain stable. Size remains roughly stable after pregnancy, but about 10% will decrease in volume by around 10%. It is important to realise that both the uterus and the fibroids increase in size by processes of hyperplasia and hypertrophy i.e. more muscle cells and greater size in muscle cells. The tissue cannot completely disappear after pregnancy but may shrink somewhat. Many women with fibroids do not have any complications during pregnancy related to the fibroid. Complications may however occur, with pain being the most common. To summarise, the effects of fibroids on pregnancy may include:
- Premature labor and delivery
- Abnormal fetal position requiring operative delivery
- Placental abruption (the placenta peels away from the lining of the uterus)
- Abnormal fetal growth
- Morbidly adherent placenta (placenta unable to be expelled after the birth)