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EARLY PREGNANCY MONITORING
hCG (human chorionic gonadotropin) is a hormone specifically produced by a pregnancy, and the detection and measurement of hCG form the basis of all pregnancy tests. hCG can be measured qualitatively (positive - present in amounts above a certain level, or negative) or quantitatively (the actual amount present measured) in both urine and blood. Blood tests are most commonly used for quantitative measurements because of their reliability. The presence of hCG can be detected within a day or two of the time of expected menses. hCG levels are used to monitor the early progression of pregnancies. As a general rule, the hCG level will approximately double every forty-eight hours in normal early pregnancies. If this rate of rise is not present, closer observation and testing may be warranted until the cause of the low levels of hCG is determined.
Vaginal ultrasound can demonstrate the presence of an intrauterine pregnancy as early as ten days after a missed period. This corresponds to an hCG level of approximately two to three thousand. Based on the initial hCG level, and taking into account the forty-eight-hour doubling time, we schedule the first ultrasound when the hCG level will be approximately five thousand. An ultrasound at this time answers several questions: Is the pregnancy in the uterus? Does it look normal? How many are there?
If the pregnancy is in the uterus, a gestational sac can be seen. This is a fluid-filled sac that on ultrasound looks like a dark hole. The gestational sac should contain a fetal pole, which is comprised of the early fetal tissue. Seeing a fetal pole tells us with a certain level of reliability that the pregnancy is probably normal. The presence of a fetal pole does not ensure 100% that the pregnancy is normal, but a relatively small percentage of pregnancies in which a fetal pole has been demonstrated will miscarry. Finally, we can see how many gestational sacs are in the uterus.
If the ultrasound fails to demonstrate a pregnancy within the uterus, an ectopic pregnancy must be suspected. If the hCG levels do not rise appropriately, the same is true. If the ultrasound demonstrates a gestational sac but no fetal pole, this is known as an empty sac, or blighted ovum. This is not a normal pregnancy (the vast majority of these have abnormal chromosomes) and is destined to miscarry.
If an ultrasound performed two to three weeks after the first ultrasound, or four to five weeks after the missed period, demonstrates that the fetus has continued to develop and a heartbeat is present, the likelihood is very high that the pregnancy will be successful.
MISCARRIAGE
Miscarriage, or spontaneous abortion, occurs in about fifteen to twenty percent of all pregnancies, regardless of how they were conceived. Most early losses are a result of the conceptus being genetically abnormal. As few as one in three human conceptions is genetically normal, but most of the genetically abnormal conceptions are lost before the woman even knows she is pregnant. Even so, some genetically abnormal conceptions do survive long enough to result in a recognized pregnancy. These are often concep-tions that have three sets of chromosomes (triploidy) rather than two, or conceptions that have an extra of just one chromosome (trisomy). These may present as an empty sac, or blighted ovum, which is a pregnancy in which there is no identifiable fetal tissue, or as a fetus that develops only briefly and then ceases. The human genetic message is very specific, and any variation from the normal set of forty-six chromosomes is rarely compatible with life.
Spontaneous abortion is, then, one possible outcome any time a conception occurs, and the chances are about one in five that any clinically recognized pregnancy will be aborted. And the chances do increase as the woman gets older. Older eggs don' divide as well when they get fertilized, and therefore the resulting pregnancies are more often abnormal. The chances of spontaneous abortion rises to as high as fifty percent in women in their early to mid-forties.
So how do we decide whether the loss of a pregnancy is just chance or the result of some other underlying problem that requires investigation? Most of the time, a single loss is attributed to bad luck unless some other factor is apparent. During their reproductive life-span, most women will experience at least one miscarriage. Should, however, two, or certainly three, losses occur without any successful pregnancies in between, evaluation is warranted. There are no hard and fast answers as to whether investigation should be initiated after two or three losses. The chances of another loss do increase slightly after two losses, particularly in older couples. Some investigation may be warranted at this time. After three losses, there is no question.
© 2005 Jarrett Fertility Group |
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