A pregnancy where the foetus does not develop properly is termed a blighted ovum. The foetus may fail to develop at all. Strange as it may seem, a foetus is not an essential part of an early pregnancy although it is appreciated that the reason for the pregnancy is the production of a foetus. Occasionally the mass of cells in the centre of the pregnancy that is destined to differentiate and develop into the foetus fails completely to get going. The whole pregnancy starts to develop normally; the chorionic villi grow on the outer side of the blastocyst and they implant in the wall of the uterus; the chorionic villi produce chorionic gonadotrophin, which stimulates the pituitary to release luteinizing hormone, which in turn provokes the corpus luteum in the ovary to produce large amounts of progesterone. Thus pregnancy is established.
At about this stage a group of cells known as the inner cell mass normally start dividing and differentiating into the different organs of the baby, but the presence of a developing foetus is not essential for the early part of pregnancy. At about the 6th week, however, the foetus should be developing its circulation and it is shortly after this, at about the 8th week of pregnancy, that the first signs that all is not well may appear since the chorionic villi must establish a circulation with the foetus so that they can form the placenta. There may be a small amount of bleeding and, as a result of a very gradual reduction in hormone levels, the woman may be aware of a slight reduction in the symptoms of pregnancy. If a circulation between the foetus and the chorionic villi is not established by about the 10th week of pregnancy, continuous or intermittent bleeding may begin, and will be followed eventually by pain and complete abortion of the pregnancy from the cavity of the uterus. Such a pregnancy contains a small amniotic sac but no foetus within its cavity.
The exact reason for a blighted ovum is not known but it is generally considered to be caused by fertilization of a normal ovum by an abnormal sperm. It is impossible to prove this theory but in the majority of instances where a blighted ovum is known to have occurred, the husband’s seminal count is usually deficient and contains more abnormal sperms than usual.
It is not known exactly how many abortions are due to blighted ova. It is however a commonly accepted view that approximately i in 5 of all human pregnancies are grossly abnormal and therefore miscarry spontaneously at about the time of the first period or they are blighted ova and miscarry at about the 8th or 10th week. Some authorities consider that blighted ova constitute 1 in 10 of ail human pregnancies. If the theories about a blighted ovum are correct, then once it has been diagnosed the husband should be examined and any abnormality in his seminal analysis corrected. However, it is an unfortunate fact that some couples are destined to produce more than their fair share of blighted ova when no abnormality can be found in either partner. In such instances there is no constructive treatment to prevent a recurrence in a subsequent pregnancy. Only rather thankless reassurance can be given that sooner or later a normal pregnancy is bound to occur and that, when it does, it will continue normally into the production of a normal infant.
Treatment for a blighted ovum can only be preventive since it can only be diagnosed after miscarriage has occurred. Women often blame their doctors, very unfairly, for treating them as though they had a normal pregnancy when their pregnancy ‘was bound to fail. If a woman who is 6 or 7 weeks pregnant starts to bleed from the vagina she will call her doctor who will diagnose a threatened miscarriage, the treatment for which is always conservative, namely bed-rest, sedation and perhaps hormone treatment. Even if the doctor has extensive tests done on the blood, the urine and the vaginal secretion, he will only learn that the pregnancy is somewhat short of hormones and that the hormone levels in the maternal body are therefore not as high as they ought to be. This abnormality may occur in a normal as well as in an abnormal pregnancy and since the doctor has no possible way of differentiating one from the other he must continue to treat the pregnancy as though it were normal. A blighted ovum is destined to fail eventually despite anything he can do. When abortion does occur it is very unfair to suggest that the doctor could have realized this and should perhaps have done something different although he is naturally aware that a couple who have lost a pregnancy find it very difficult to appreciate the medical facts.