Rh blood type and antibody screen in pregnancy
Early in pregnancy, a blood test finds your blood type and whether you are Rh positive or Rh negative. If you are Rh negative, an antibody screen shows whether your body has made antibodies to Rh-positive blood. (ACOG)
Why it is checked
Rh incompatibility develops when a pregnant woman has Rh-negative blood and the baby in her womb has Rh-positive blood. (MedlinePlus, 2025) When blood from an Rh-positive fetus gets into the bloodstream of an Rh-negative woman, her body may make anti-Rh antibodies. These can cross the placenta and attack the fetus's blood cells, causing a serious type of anemia, and can cause jaundice in a newborn. (ACOG) MedlinePlus says blood typing is very important during pregnancy, because careful testing can prevent severe anemia in the newborn and jaundice. (MedlinePlus, 2026)
A small amount of blood from the fetus can mix with the pregnant person's blood during labor and birth. ACOG says it can also happen with amniocentesis or chorionic villus sampling (CVS), bleeding during pregnancy, attempts to turn a breech fetus, and trauma to the abdomen during pregnancy. (ACOG)
When the tests are done
- First prenatal visit: the USPSTF strongly recommends Rh(D) blood typing and antibody testing for all pregnant women at their first visit for pregnancy-related care (grade A). (USPSTF, 2004)
- 24 to 28 weeks: it recommends repeating the Rh(D) antibody test for all unsensitized Rh(D)-negative women, unless the biological father is known to be Rh(D)-negative (grade B). (USPSTF, 2004)
- Status: the February 2004 statement is still the current USPSTF recommendation. (USPSTF, 2004) ACOG's Practice Bulletin 181 on preventing Rh D antibodies, from August 2017, was reaffirmed in 2026. (ACOG PB 181)
The other routine tests at the first visit and at 24 to 28 weeks are on pregnancy screenings by week.
How the test is done
A simple blood test finds your blood type and Rh status, usually in your ob-gyn's office at the first prenatal care visit. (ACOG) No special preparation is needed. In the lab, your blood is mixed with antibodies to see whether the cells stick together; Rh typing uses a similar method. You will be told your ABO blood type (A, B, AB or O) and whether you are Rh positive or Rh negative. (MedlinePlus, 2026)
What the results mean, in plain words
| Result | What the sources say |
|---|---|
| Rh-positive | Your red blood cells have the Rh factor protein. Most people are Rh positive. Rh problems in pregnancy occur when the pregnant person is Rh negative and the fetus is Rh positive. (ACOG) |
| Rh-negative | Your red blood cells do not have the Rh factor protein. If your fetus is Rh positive, this is called Rh incompatibility. Treatment can be given to prevent these problems, and ACOG says the aim is to find out early in pregnancy whether you are Rh negative. (ACOG) (MedlinePlus, 2026) |
| Antibody screen negative | No antibodies to Rh-positive blood were found. For an Rh-negative person who has not made antibodies (unsensitized), the USPSTF recommends repeating the antibody test at 24 to 28 weeks, unless the biological father is known to be Rh-negative. (ACOG) (USPSTF, 2004) |
| Antibody screen positive | An Rh-negative person has made antibodies to Rh-positive blood; the test can also show how many. The preventive shot does not help once antibodies have been made. The well-being of the fetus is then checked during the pregnancy, usually with ultrasound exams. (ACOG) |
Why the other parent's blood type may come up
The Rh factor is passed from parent to child through genes, and the fetus can inherit it from the father or the mother. If the fetus does not inherit it from either parent, the fetus is Rh negative. (ACOG) That is why the USPSTF's repeat antibody test applies unless the biological father is known to be Rh-negative, (USPSTF, 2004) and why MedlinePlus says the preventive shot is given when the father is Rh-positive or his blood type is not known. (MedlinePlus, 2025)
The preventive shot, in general terms
The goal is to stop an Rh-negative person from making Rh antibodies in the first place, by finding out early whether they are Rh negative and, if needed, giving a medication by injection that prevents antibodies from forming. (ACOG) Sources say it is offered at set times during pregnancy and after the birth of an Rh-positive baby, and after events such as a miscarriage or abortion, amniocentesis or CVS, bleeding, or trauma to the abdomen. (ACOG) (MedlinePlus, 2025) It works only for the pregnancy for which it is given, so it is needed again in each pregnancy, and it does not help once antibodies have been made. (ACOG) ACOG's Practice Bulletin says the routine use of this medication is responsible for the reduced rate of these antibodies in more economically developed countries. (ACOG PB 181)
Your doctor decides what your result means for you, and whether and when you need the shot. This page does not give treatment advice. If a result worries you, see after an abnormal screening result for questions to ask.
When to contact a provider
After birth, an affected infant may have yellowing of the skin and whites of the eyes, low muscle tone and lethargy. (MedlinePlus, 2025) Newborn checks are on newborn screening results. MedlinePlus says: (MedlinePlus, 2025)
Contact your health care provider if you think or know you are pregnant and have not yet seen a provider.
Where they differ:
- First antibody screen: the USPSTF recommends antibody testing for all pregnant women at the first visit; (USPSTF, 2004) ACOG's patient FAQ says that if you are Rh negative and your fetus may be Rh positive, your ob-gyn may request it in the first trimester. (ACOG)
- The repeat test: the USPSTF says 24 to 28 weeks for unsensitized Rh(D)-negative women; (USPSTF, 2004) ACOG says you may have the antibody screen again at 28 weeks, and in some cases more often. (ACOG)
- UK practice: NICE says to offer a blood test for blood group and rhesus D status at the first face-to-face antenatal appointment, and at 28 weeks to offer a blood test for blood group and antibodies, plus the preventive treatment to rhesus D-negative women who are not known to be sensitised. (NICE NG201)
Questions people ask
What does the Rh factor mean?
The Rh factor is a protein that can be found on the surface of red blood cells. If your blood cells have it, you are Rh positive; if not, you are Rh negative. The positive or negative part of a blood type such as O positive or A negative refers to Rh status. (ACOG)
When is the Rh blood type test done in pregnancy?
The USPSTF recommends Rh(D) blood typing and antibody testing for all pregnant women at the first visit for pregnancy-related care. ACOG says the sample is usually taken at the first prenatal care visit. (USPSTF, 2004) (ACOG)
Why is the antibody test repeated at 24 to 28 weeks?
For Rh-negative people who have not made antibodies, the USPSTF found that a repeat test, unless the father is known to be Rh-negative, adds benefit over a single test at the first visit. (USPSTF, 2004)
Is a first pregnancy affected by Rh incompatibility?
Health problems usually do not occur in an Rh-negative woman's first pregnancy with an Rh-positive fetus, because her body does not have a chance to make a lot of antibodies. A later Rh-positive fetus can be at risk if antibodies were made. (ACOG)
Why does my provider ask about the baby's father's blood type?
The fetus can inherit the Rh factor from either parent. The USPSTF repeat test applies unless the biological father is known to be Rh-negative. (ACOG) (USPSTF, 2004)
How common is being Rh-negative?
ACOG's Practice Bulletin gives rates of Rh D-negative people from 5% in India to 15% in North America. (ACOG PB 181)
Do I need to prepare for the blood test?
No special preparation is needed for blood typing. (MedlinePlus, 2026)