Misc.kids Frequently Asked Questions
Pre-Pregnancy and Pregnancy Tests
Collection maintained by: Lynn Gazis-Sax (email@example.com)
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Pre-Pregnancy and Pregnancy Tests. Please try to be as concise as possible,
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Copyright 1995, Lynn Gazis-Sax. Use and copying of this information are
permitted as long as (1) no fees or compensation are charged for
use, copies or access to this information, and (2) this copyright
notice is included intact.
[NOTE: this is information collected from many sources and while I
have strived to be accurate and complete, I cannot guarantee that I
have succeeded. This is not medical advice. For that, see your
doctor or other health care provider.]
Many people helped with the prenatal testing FAQs by advising about
the best way to structure them, by contributing stories and information,
or by reviewing versions of the FAQs. A list of acknowledgements can
be found in the Prenatal Tests: Overview FAQ.
II. Prepregnancy and pregnancy tests
1. What screening tests can be done prior to pregnancy and when should
they be done?
From Robbrenner@aol.com (Robert Brenner MD)
II 1. Screening tests prior to pregnancy: Measles and Rubella immunity
tests. HIV. STD(can be done early in pregnancy). Tay-Sachs.
[And, in answer to further questions from me]
1)STD stands for sexually transmitted diseases.
2)If your immune to rubella on premarital blood work, it probably is not
necessary to repeat the test. It will be repeated however with each
4)Group B strep is a controversial area. The Group B strep is a bacterium
which can be seen in 15-20% of normal pregnant women. Studies have been done
with routine prenatal cultures and if positive then treatment. The
recurrence rate after treatment is quite high. Also, some women will culture
negative at one time and in fact have the Group B strep bacteria at a later
date. Even if a woman carries the strep it usually does not affect her baby.
The present recommendation of the American College of OB-GYN is not to do
routine cultures as they are inaccurate and not cost effective. Patients
should be cultured and treated if they are in pre-term labor, if they have
ruptured membranes for over 16 hours, if they are febrile while in labor, or
if there is a previous history of delivering a baby infected with the Group B
Strep. Present research is in the area of finding either a vaccine against
the Group B strep or finding a rapid diagnostic test that can be done on all
patients in labor. [Added note from LGS: Further information about Group B
strep can be found at http://www.childbirth.org/articles/comp.html.]
There are a variety of different carrier tests, including, but not limited
to: Tay-Sachs, sickle cell, thalassemia, fragile X, alpha1 antitryptiphine
deficiency, glucose-6-phosphate dehydrogenase deficiency, and less precise
ones for Duchenne muscular dystrophy and hemophilia (Nelson Textbook of
Pediatrics). Sickle cell anemia is chiefly found in people of African
descent. Tay-Sachs is chiefly found among Eastern European Ashkenazi Jews
and French Canadians. Thalassemia is several hemoglobin disorders, found
among people of Mediterranean or Southeast Asian descent. For these,
carrier screening is offered to peple of the appropriate ethnic
background. Other carrier screening tests may be offered if family
history warrants it.
1a. What are some cases where early recipients of a vaccine may lose
immunity, or people who were screened early for carrier status (e.g. for
Tay Sachs) may have invalid results? At what date was an acceptable test
or vaccine formulated?
From Tracy Lee Murphy:
Could you look up three things for me?
Sure, here we go. I can send you copies of the citations if
necessary, but for the sake of brevity I'll keep it short.
1) The early measles vaccine was not as effective as the current one.
People vaccinated before a certain date will have been vaccinated
with the less effective version. I have misplaced my note about what
the year was that the vaccine was improved. Could you find that out?
>Study pub JAMA 1990 264(19):2529-2533
>Measles outbreak causes: vaccinations given before age of 15 months
>and vaccinations before a change in the measles VACCINE STABLIZER
2) Could you check whether there was any similar problem with an
early version of the rubella vaccine? I heard a net rumor to that
effect, but all I have is that an MMR booster has been added to the
schedule which wasn't there originally. It could be that the person
who emailed me had heard from someone who confused the measles and
rubella vaccines, but I want to check.
>I will assume that this was a measles/rubella mixup. The journals
>even seem to treat them as one subject. Everything I'm seeing says
>that a revaccination in high school is necessary even if the child
>got the early childhood set of shots.
3) Same question for Tay Sachs. A carrier screening test came out
in 1971. Was the early carrier test the same as the current version,
or was it less reliable (in which case people whose parents got results
saying they were not carriers might still want to be screened themselves)?
>I found a variety of highly technical articles on Tay Sachs (which
>proteins/antibodies, Jewish/Jewish v. Jewish/Irish testing, etc.)
>I don't want to count on my non-scientific method of scanning journal
>articles on this. The articles I understood said that *most*
>parents (Jewish) don't do testing unless a family member has had a
>Tay Sachs child and that education was still needed (1992 study).
>It does sound like there are a couple of different Tay Sachs tests
>used by ?different labs/doctors/countries?
>I don't feel too good about this info, sorry.
This is for a FAQ on prenatal tests (though the first two would also
be relevant for the Childhood Vaccination FAQ).
>I hope this helps. If you need more, just drop me a line.
tracy lee murphy
1b. What diseases should be tested for prior to pregnancy?
1c. What about screening for venereal disease?
See above. There are also some net resources for further information
about sexually transmitted diseases. The following Worldwide Web
directories contain information about sexually transmitted diseases
(under various document names):
One reason to screen for AIDS in particular is evidence that AZT, when
administered to pregnant women, can dramatically reduce the incidence
of maternal-fetal HIV transmission. In August of 1994, the FDA approved
AZT for use in preventing transmission of HIV from HIV-infected pregnant
women to their babies, as a result of data from a federally sponsored
study. "In this randomized, placebo-controlled trial, HIV-infected
women received 500 mg of AZT per day orally during pregnancy and a
continuous intravenous infusion of AZT during labor. Therapy was begun
between 14 and 34 weeks after conception. . . . The study was halted when
a planned interim review of the data showed that for women treated with
AZT the estimated rate of transmitting the virus to their babies was
reduced by approximately two-thirds, from 25.5 percent infected babies
from women on placebo to 8.3 percent infected babies from women on the
AZT regimen. A long-term followup study of babies exposed to AZT is under
way." (Source: HICN739 Medical News, August 25, 1994.)
2. What is HCG and what is its significance in pregnancy testing?
2a. How early can a pregnancy test be done?
2b. How likely is a false negative in an early pregnancy test?
2c. What over the counter pregnancy tests are most accurate?
From Robbrenner@aol.com (Robert Brenner MD)
2. HCG is human chorionic gonadotropin. It is secreted by the placenta and
is measured by pregnancy tests. Urine pregnancy tests can turn positive as
early as 2 days after a missed period. I recommend doing a urine pregnancy
test when 1 week late for the period to lesson the incidence of false
negative results. Serum pregnancy tests can turn positive around the time of
the missed period but again I wait til the patient is 1 week late to avoid
false negative results. Essentially all over the counter pregnancey tests are
the same. In a normal pregnancy HCG levels should double every 3 days. This
is measured by quantitative serum HCG tests.
2d. My HCG level is not rising as quickly as it is supposed to? What is
the normal range, and how worried should I be?
From Robbrenner@aol.com (Robert Brenner MD)
HCG titers double in 3 to 4 days in a normal pregnancy. If HCG titers drop,
the ball game is over and the pregnancy is non-viable. HCG titers that
plateau or do not double suggest either a pregnancy that is destined to abort
or an ectopic. If there is any question, I like to get a serum progesterone.
Progesterone of 15 ng/ml or more is compatible with a normal intrauterine
pregnancy. Under 10 suggests an abnormal pregnancy.
Once the HCG titer is 1000ng/ml or more, an intrauterine gestational sac
should be seen on endovaginal sonogram. If a gestational sac is seen, this
rules out ectopic. By 6 weeks from the last menstrual period, a yolk sac
should be seen on vaginal sonogram and by 6-7 weeks a fetal heart beat should
be seen. All these parameters can be used to assess the viability of an
intrauterine pregnancy. However, one must not delay too long if an ectopic
cannot be completely ruled out.
A Beta HCG chart can be found at http://www.mnsinc.com/inciid/inciid.html.