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What Chemical Pregnancies Indicate
Prior to suffering a loss or just hitting roadblocks in conceiving, most people may blessedly think that all conception leads to pregnancy. Unless a woman has gone through fertility treatments or suffered an early pregnancy loss herself, it's likely she may be unfamiliar with the terms 'clinical pregnancy' or 'chemical pregnancy'. As a matter of fact, unless she has been closely monitored following conception, it's entirely possible a woman could have had a chemical pregnancy herself without being aware of it - it is such an early loss that it happens before or around the expected period.
So what exactly is a chemical pregnancy? How common are they really? Does having one make any implications about where the journey to parenthood is likely to take you? To answer some of these questions, I spoke to Dr. Carl Herbert, Reproductive Endocrinologist and fertility specialist at Pacific Fertility Center in San Francisco.
To get an understanding of what a chemical pregnancy is, exactly, it's helpful to look at what happens to the body immediately following conception.
"When a sperm and an egg unite and the resulting embryo starts to grow, special cells known as cytotrophoblast cells (the placenta) manufacture and secrete pregnancy hormone (human Chorionic Gonadotropin--hCG)," Dr. Herbert explains. " Measuring this hormone (hCG) in a woman’s blood or urine is the first documentation of a pregnancy. As the number of placental cells increases, more hCG is secreted. Using quantitative measurements of blood hCG values, one can estimate the health and viability of an early pregnancy. During the first several weeks of a pregnancy, the value of hCG in a woman’s blood should approximately double every 48 hours. This is known as the “doubling time” and can help in the early diagnosis of an eventual miscarriage or an ectopic pregnancy. Remember, hCG, i.e., pregnancy hormone is derived from placental cells, not fetal cells. Therefore, if the placenta grows but the fetus does not, the hormone values may remain normal for a period of time."
So if a pregnancy is not viable, the hCG levels don't rise within a 48 hour period as they should. If that's true of all miscarriages, what is the difference between a chemical pregnancy and a clinical pregnancy?
"Once a pregnancy has progressed to about five weeks gestational age, the embryonic sac becomes visible on ultrasound examination. After the sac is seen on ultrasound, the pregnancy is labeled a “clinical” pregnancy. A conception, which has measurable hCG but does not develop far enough to be seen on an ultrasound, is considered a “chemical” pregnancy. Therefore, all chemical pregnancies are, by definition, unsuccessful and the only evidence that an early pregnancy existed is the measurement of hCG in a woman’s blood or urine."
There is a lot of available information online regarding what the miscarriage of a clinical pregnancy could possibly mean in terms of a woman's overall ability to carry a pregnancy to term. There seems to be less information, however, on how telling a
chemical pregnancy can be about whether or not it's indicative of problems with future pregnancies. Do chemical pregnancies 'mean anything' or are they something that 'just happens'? Are there women who are more likely to have them?
"In natural conception cycles, a chemical pregnancy does document the ability of sperm to fertilize an egg and early embryo attachment (implantation)," says Dr. Herbert. "In ART cycles, the fertilization can be observed in the laboratory. However, after transfer, a chemical pregnancy will at least document an early embryo attachment in the uterus. The inability of a pregnancy to progress from a chemical to a clinical pregnancy may be related to either the embryo itself or the uterine environment. If an embryo is chromosomally abnormal, it may well have limited potential to grow and stop developing quite early in a pregnancy. Chromosomally abnormal embryos can occur in a woman at any age; however, they are more likely to occur as a woman ages, especially if she conceives in her late 30s and beyond. In our IVF program there is about a 40% chemical pregnancy rate for women over the age of 40 but only a 20% rate for women less than 35 years and a less than 10% rate for women using egg donation. These differences, based on age, mostly reflect the changes in egg quality which decreases with increasing age."
Apart from egg quality, could a chemical pregnancy hint to a possible diagnosis or condition?
"A chemical pregnancy might also occur because of the uterus or endometrial lining is inadequate to support full pregnancy development," he adds."Conditions such as uterine fibroids; congenital uterine malformation such as uterine septum; endometrial polyps; or hormonal abnormalities which create “luteal phase defects,” i.e., poor endometrium development, can all be causally related to early pregnancy failure leading to a chemical pregnancy outcome."
So there are treatable conditions within a woman's body that could be the cause of a chemical pregnancy. Are there any indications that a male factor could be a cause?
"There remains significant controversy and inadequate scientific knowledge about the effect of sperm quality on embryo quality and implantation," he explains. "However, it is possible that sperm or male factor infertility could contribute to the production of chemical pregnancies which do not progress normally."
If a woman has one chemical pregnancy, should she be worried about what that says about future pregnancies? Is it in any way indicative of what may come down the road?
"If a young woman conceives naturally but experiences a chemical pregnancy loss, she should be evaluated for a possible cause taking into consideration the previously mentioned issues. However, if her evaluation does not reveal an obvious cause, the likelihood of success in the subsequent pregnancy is quite high," Dr. Herbert explains. "However, if a woman of more advanced reproductive age, i.e., greater than 38 years with known egg compromise experiences a chemical pregnancy loss, especially if she conceives in an ART cycle, the outlook for future success is somewhat decreased. This loss is often confirming an egg issue which may become a repetitive problem. If a woman demonstrates repetitive chemical pregnancy losses, it is a bad prognostic sign and aggressive evaluation needs to be completed with hopes of defining a treatable cause. If such a cause is not found, a random subsequent pregnancy might get beyond the chemical stage, but odds for a successful pregnancy are definitely decreased."
If you have experienced miscarriage, schedule a consultation with a fertility doctor, or type in your zip code in the “Find a Doctor” or “Find a Clinic” search on our website.