David has blogged in the past about the diagnosis of gestational diabetes mellitus (GDM). In July 2012 he discussed a debate that was underway among experts regarding newly proposed diagnostic guidelines. Just to recapitulate the debate, for at least 10 years we have been diagnosing GDM with a two-step process.... Continue reading

In the last several years, there have been a lot of articles in both the popular press and the scientific literature about Vitamin D. There are studies that report that low concentrations of vitamin D are associated with everything from cancer to multiple sclerosis and asthma to cardiovascular disease. There... Continue reading

There is a saying in science that every 10 or 20 years scientists "reinvent" things. This refers to observations someone made and published, but the findings were largely ignored for 10-20 years until a new scientist comes along and makes the same or similar observation and suddenly everyone takes notice.... Continue reading

In September 2011, The American Thyroid Association (ATA) published new guidelines on the diagnosis and management of thyroid disease during pregnancy and postpartum. There are many recommendations in the guidelines, but I wanted to highlight one in particular. Recommendation 2 "If trimester-specific reference ranges for TSH are not available in... Continue reading

The short answer is no, but let me explain why. Iodine is necessary for the production of the thyroid hormones T3 and T4. A deficiency of iodine leads to decreased production of these hormones and can cause goiter (enlargement of the thyroid) and hypothyroidism. During pregnancy, a number of normal... Continue reading

Women in their mid to late 30s and early 40s with infertility constitute the largest portion of the total infertility population. These women are also at an increased risk for pregnancy loss. This reflects a decline in oocyte quality and a diminished ovarian reserve as a result of follicular depletion.... Continue reading

Recently, I blogged about TORCH testing (sometimes called TORCHES). The "S" in TORCHES stands for Syphilis. Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum. Syphilis can present in one of four different stages: primary, secondary, latent, and tertiary. Many people infected with syphilis are asymptomatic,... Continue reading

A few months ago, I wrote about thyroid testing during pregnancy. As I mentioned, there was a study published in 1999 that examined the association of hypothyroidism in mothers and the neurocognitive development in their children. The study demonstrated that, at 7-9 years of age, children from the women with... Continue reading

TORCH testing (sometimes called TORCHES testing) includes tests for a group of infectious diseases that can infect pregnant women and cause birth defects or death in their infants. TORCHES is an acronym for the following infectious diseases: Toxoplasma gondii (toxoplasmosis)- a parasite that can be acquired from ingesting cysts from... Continue reading

Although the hCG diet is slightly outside of the realm of The Pregnancy Lab, we have discussed it in the past because we get questions about it all the time. Don't even consider doing this diet to shed your extra holiday pounds. On December 6, 2011, the FDA and Federal... Continue reading

False Negative Pregnancy Tests A false negative pregnancy test means that the test tells the patient they are not pregnant when they really are. Why does this occur? There are four well known reasons pregnancy tests can give false negative results. 1) The most common reason is testing too early after fertilization occurs. The pregnancy hormone, hCG is not produced until implantation occurs and it takes several days for the hCG concentrations to get high enough in blood and then urine to give a positive signal. Most devices give positive results around the day of a woman's expected period, but this can vary widely. 2) Another reason for false negative results is dilute urine. If a woman drinks a lot of fluids, the concentration of hCG in the urine will be more dilute. For this reason many doctors recommend that testing be performed on the first urine of the morning because this tends to be the most concentrated (because you probably have not drank anything all night long). 3) A very rare cause of false negative results occurs when very, very, high concentrations of hCG are present. This is called the "hook effect". The hCG assays works by forming a so-called "sandwich" with two different antibodies as the "bread" and the hCG molecule as the "meat". The hook effect occurs when the hCG concentration is so high that it saturates both antibodies and there are so many molecules that the antibodies don't actually form a sandwich. This is rare because women don't normally produce enough hCG to saturate both antibodies. The hook effect should be of concern in a hospital setting, but most women should not be concerned about a hook effect with their urine. A hook effect can be confirmed if testing shows a positive result after sample dilution. 4) Finally, the other reason for false negatives was only recently described and is referred to as the "variant hook effect". This is much more common than the hook effect. As pregnancy progresses, there are actually different variant forms of hCG that begin to appear in the urine. After about 5 weeks of pregnancy (i.e. 3 weeks after the expected period) concentrations of hCG beta core fragment are higher than all other forms of hCG. This is perfectly normal. Unfortunately, the concentration of hCG beta core fragment can saturate one of the antibodies used in the assay in certain pregnancy kits, and the other antibody doesn't recognize the beta core fragment. As a result, no sandwich forms and the test is read as a negative. The farther in pregnancy a woman is, the more likely that this false negative will occur. Similar to the hook effect, the variant hook effect can be confirmed if testing shows a positive result after diluting the sample. Continue reading