Prenatal - Routine Laboratory Tests

We call prenatal medical consultations during pregnancy, which aim to monitor the pregnancy and ensure good health to the fetus and the expectant mother.

Pregnant woman
Pregnant woman

The prenatal consultations must be initiated in the first quarter, preferably up to the 10th week of pregnancy. In general, we encourage women to schedule a prenatal follow-up visit as soon as they discover that they are pregnant.

Prenatal aims to:
  • To estimate the correct gestational age and expected date of delivery.
  • To identify, prevent or treat potential problems that could endanger the pregnancy.
  • Monitor during pregnancy the health of the mother and fetus.
  • Inform and educate mother on healthy and proper habits during pregnancy.

Laboratory exams in prenatal

Several laboratory tests, both blood and urine are needed for proper prenatal care. We will then explain simply prenatal tests most requested during pregnancy.

Prenatal examinations of 1st quarter: typing blood

Blood typing is important to detect women who have blood to Rhesus negative (A-, B-, AB- and O-) of infants who are pregnant Rh-positive (A +, B +, AB + or O +).

In general, the baby's blood does not mix with the mother's blood during pregnancy, so in a first pregnancy there are no problems when the mother and child have different blood factors. However, during delivery, the mother's body can get in touch with some fetal blood portion, stimulating maternal immune system to produce antibodies against the Rh factor. This means that in a next pregnancy, the mother's immune system may reject a fetus with positive Rh factor, a serious complication known as fetal erythroblastosis.

Therefore, all pregnant women with Rh negative factor that is pregnant with a baby with Rh positive should receive immune globulin shot in the third quarter and in the first 72 hours after delivery, in order to prevent the mother's immune system to produce permanent antibody the Rh factor.

Pregnant women who have a positive Rh factor in the blood does not have to worry about this type of complication in pregnancy.

Prenatal examinations of 1st quarter: pap smear

The gynecological Pap smear, also called cervical cytology is used for screening of cervical cancer. Every woman should have this test on a regular basis and the fact of being pregnant does not change this routine. So in general, it is suggested that all women over 21 years old, who is pregnant and has not done pap smear recently, do the pelvic exam at the first visit the prenatal.

The common gynecological examination also serves to detect signs of landslides or colpitis or cervicitis that may suggest a gynecological infection in progress. All discharge with suspicious appearance should be investigated.

Prenatal examinations of 1st quarter: blood count

The blood count during prenatal has as main objective the investigation of anemia, which in pregnant women is set when the hemoglobin level is below 11 g/dL or hematocrit less than 33%.

Pregnant women usually retain fluid and there is a natural dilution of the blood, causing normal hemoglobin level is a bit lower than in nonpregnant women, whose lower hemoglobin normal limit is 12 g/dl and hematocrit is 36%.

Therefore, every pregnant may have a mild anemia because of increased blood volume of water, without this having clinical relevance. In pregnant, only hemoglobin below 11 g/dl are worrying and should be treated.

The blood test is usually requested in the first query and can be repeated, the physician's discretion, in the second and third trimester of pregnancy.

Prenatal examinations of the 1st and 3rd quarter: blood glucose

The blood glucose level (blood glucose concentration) in prenatal serves to find the gestational diabetes mellitus. There is no consensus among the various international midwifery schools on the best way to track and diagnose gestational diabetes. What we present below are the guidelines FEBRASGO (Brazilian Federation of Gynecology and Obstetrics). The American and European companies use slightly different methods and values.

The basic screening is done with a fasting glucose at first visit and an oral glucose tolerance test between the 24th and 28th week.

The value considered normal blood glucose in the first consultation fasting is up to 85 mg/dl. The criteria for the diagnosis of diabetes is a value above 126 mg/dl (the test should be repeated to confirm the value).

Pregnant women with blood glucose between 85 and 125 mg/dl are those at high risk for developing gestational diabetes to pregnancy and logo should be very careful with food and weight gain during pregnancy.

All pregnant women with glucose levels between 85 and 125 mg/dl and those with lower blood glucose 85 mg/dl, but with risk factors (such as family history, obesity, gestational diabetes in a previous pregnancy, etc.) should do the test oral tolerance, also called glycemic index, between 24 and 28 weeks of pregnancy.

The test is done by 3 doses of glucose. The first is taken in the fasting state. Immediately after harvesting the blood, the mother ingests a syrup containing 75 grams of glucose and reaps 2 more blood samples, 1 and 2 hours after drinking the syrup. the following expected results are:
  • Fasting Glycemia: Normal up to 95 mg/dl.
  • Glycemia after 1 hour: Normal 180 mg/dl.
  • Glycemia after 2 hours: Normal up to 155 mg/dl.

If the mother has 2 of the 3 above values changed, it can already be considered as having gestational diabetes.

Prenatal examinations 1st, 2nd and 3rd quarter: urine test

Two urine tests are part of the basic assessment of prenatal care: EAS (Urine type 1) and urine culture.

The EAS is a simple urinalysis, which serves primarily to detect bleeding, pus (white blood cells) or protein in the urine. It is usually requested in the first and third quarter.

The presence of blood or pus may be a urinary tract inflammation signal, especially urinary tract infection. Have proteinuria, which is the name we give when there is the presence of protein in the urine is one of the possible signs of preeclampsia, a disease that may arise in the 3rd trimester.

In a survey of simple urine, research of leukocytes, erythrocytes and proteins must be negative. If the result of this research is provided in numbers, they must be below the reference value.

The urine culture is a test to identify specific bacteria in urine. The presence of bacteria in the urine of pregnant even without any symptoms of urinary tract infection, should always be treated with antibiotics because it increases the risk of pregnancy complications.

Both the EAS as a urine culture often requested in the three trimesters of pregnancy.

Infections search in prenatal

Another important point is the prenatal screening of infectious diseases that can cause complications in pregnancy. Infections such as toxoplasmosis, rubella, syphilis, herpes and others are acquired DURING pregnancy can cause miscarriage, premature birth or ma- formation of the fetus.

So it is important to conduct called serology blood tests that check the presence of antibodies in the mother's blood against these infections. Diseases whose pregnant already have specific antibodies can not be acquired again, with no risk of infection during pregnancy. For example, have had rubella at some point in life is not the problem, however, because it means that the mother is immunized and not at risk of getting infected again. The problem is never having had rubella and the disease DURING pregnancy.

Prenatal Serology must be requested in the first query. All infections whose pregnant have negative serology, i.e. has no specific antibodies, serology should be repeated in the second and third quarter to make sure that the mother is not infected during the pregnancy.

IgG and IgM antibodies in pregnancy

In general, antibodies are screened on serology IgG and IgM. An IgM antibody means that the patient has acquired the infection recently. Since the IgG antibody is a memory, which arises weeks after the patient has been infected. Therefore, we have the following situations:
  • Positive IgM and IgG negative: this result indicates recent infection. If this kind of serology arise during pregnancy, pregnancy is at risk.
  • Negative IgM and IgG positive: This result suggests old and already cured infection. This type of serology indicates that the patient has had a long illness, was cured and now is immunized without risk of having it again. It is the best outcome for pregnant women.
  • Negative IgM and IgG negative: this result indicates that the pregnant never had the disease. This type of serology suggests that the patient is not sick but do not have immunity against infection, can contract it, if exposed to the germ during pregnancy.

Example of a fictitious pregnant:
  • Serology for toxoplasmosis: Negative IgM and IgG negative.
  • serology Rubella: negative IgM and IgG positive.
  • Serology for cytomegalovirus: negative IgM and IgG positive.

The above results indicate that the mother never had toxoplasmosis, but is already immunized against rubella and cytomegalovirus. This means that the only risk it during pregnancy is in relation to toxoplasmosis. The obstetrician just need to guide her on how to minimize the risk of contracting toxoplasmosis. In the next quarter, there is no need to repeat the serology rubella or cytomegalovirus, only against toxoplasmosis.

It is important to note that not all serology results come with IgG and IgM dosages. In the case of HIV, for example, the result is only as reagent (positive) or nonreactive (negative).

Serology routine requested prenatally

Serology for some infections are routine in any prenatal care. They are:

The above infections are those that should be researched routine in low-risk pregnancies. Other serological tests may be requested if there is need, for example, a pregnant woman who has had recent contact with people with chickenpox, herpes or mumps, for example.

What we explained in this article are only the most simple laboratory tests of prenatal care. In case of high-risk pregnancy or pregnant women with risk factors or a strong family history of other diseases, it is the obstetrician's obligation to make a more specific investigation.

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