Scar tissue, also known as adhesions, can cause pregnancy complications when it forms in, on or around the uterus or fallopian tubes. Adhesions form as the result of trauma, such as surgery or infection. Scar tissue can interfere with the embryo's ability to implant and grow or can cause problems with the placenta that affect the pregnancy.
The chance of miscarriage or repeated miscarriage in early pregnancy is increased if Asherman's syndrome, scarring of the inside of the uterus, is present, the American Society for Reproductive Medicine states. Late fetal loss may also occur. Asherman's syndrome may develop after dilatation and curettage, especially if it is done immediately following a pregnancy, after cesarean section or after fibroid removal.
Woman with uterine scars from surgery, such as previous cesarean section or fibroid removal, are more likely to have uterine rupture during pregnancy. A rupture can be small or large enough to threaten the life of mother and baby.
Uterine rupture occurs in two in 1,000 women in a repeat cesarean section and five in 1,000 during vaginal birth after cesarean (VBAC). Women with a vertical scar on the uterus are much more likely to rupture; vertical scars rupture in between 40 and 90 of 1,000 women. A second cesarean increases the subsequent risk of rupture; this occurs in 37 of 1000 women in a third pregnancy, states Kathe Gallagher, MSW, in the University of California San Diego Healthwise article entitled "Rupture of the Uterine Scar and VBAC."
Scar tissue in the fallopian tubes damages the cilia, the small hairs that move the egg down the tube, and increases the chance that an embryo will implant in the fallopian tube rather than in the uterus. Tubal implantation is known as ectopic pregnancy.
Ectopic pregnancies are not viable; the tube isn't large enough to accommodate a growing fetus. Ectopic pregnancies are also dangerous for the mother; the tube can rupture, and acute bleeding can result; tubal rupture is life-threatening if not recognized promptly and treated by surgery to remove the tube.
Placental problems, such as placenta accreta, in which the placenta adheres to the uterine wall and can't be removed, are more common in women with scarring from Asherman's syndrome, Kenneth Trofatter, M.D. states. Placenta previa, in which the placenta implants too low on the uterine wall and completely or partially covers the cervix, can lead to possible hemorrhage and also is more common in women with Asherman's syndrome.