Fundal height is always measured in centimeters. Your doctor will use a flexible measuring tape to measure the distance from your pelvis area to the top of your uterus. This is about where your belly slopes downwards after going over the highest point of your bump. This quick measurement is not just a really good party trick —measuring the fundal height can help tell a few important things about your pregnancy:.
So if your fundal distance is about 26 centimeters plus or minus 2 centimeters , you are probably around week 26 of your pregnancy. The fundal height is so important that researchers made an international formula to help better estimate pregnancy weeks and baby size with this measurement.
There are several reasons why this might happen:. If your fundal height is too long, your doctor will double-check the measurement and may also give you an ultrasound scan. Some babies are just longer or bigger than average. How many weeks pregnant is the woman in each case, based on the finger method of measuring fundal height shown in Figure In Figure The measurement in Figure Look at your own hands.
Because of the big variation in the thickness of our fingers, there could be up to three weeks difference between the fundal height measurement of the same woman made by two different people. Even if the same health worker measures the fundal height of the same woman several times on the same day, the answer may be different each time, because the finger method is not very precise.
Finally, you might have realised that the distance between the symphysis pubis pubic bone and the umbilicus bellybutton varies between women when they are not pregnant, and this variation affects the accuracy of the fundal height measurement using the finger method. To overcome these limitations, it is recommended that you measure fundal height using a soft tape measure if you have one, as described next. During the second half of pregnancy, the size of the uterus in centimetres is close to the number of weeks that the woman has been pregnant.
For example, if it has been 24 weeks since her last normal menstrual period, the uterus will usually measure cm. The uterus should grow about 1 cm every week, or 4 cm every month. Doctors, nurses and many midwives are taught to count pregnancy by weeks instead of months. They start counting at the first day of the last normal menstrual period LNMP , even though the woman probably got pregnant two weeks later. Counting this way makes most pregnancies 40 weeks long or you can say a normal gestation is 40 weeks.
If you are measuring correctly and you do not find the top of the uterus where you expect it to be, based on the date the woman gave you for her LNMP, it could mean three different things:. There are several reasons why a due date figured from the LNMP could be wrong.
Sometimes women do not remember the date of their LNMP correctly. Sometimes a woman misses her menstruation for another reason, and then gets pregnant later. This woman could really be less pregnant than you thought, so the uterus is smaller than you expect.
Or sometimes a woman has a little bleeding after she gets pregnant. If she assumed that was her LNMP, this woman will be one or two months more pregnant than you thought. The uterus will be bigger than you expect.
Remember due dates are not exact. Women often give birth up to 2 or 3 weeks before or after their due date. This is usually safe. If the due date does not match the size of the uterus at the first visit, make a note. Wait and measure the uterus again in two to four weeks. If the uterus grows about two finger-widths or 1 cm a month, the due date that you got from feeling the top of the uterus is probably correct.
The due date you got by counting from the LNMP was probably wrong. If the uterus grows more than 2 finger-widths a month, or more than 1 cm a week, several different causes are possible:. If you think there might be twins, even if you can find only one heartbeat, refer the woman to the nearest health centre. It can be very difficult to know for sure that a mother is pregnant with twins.
Signs of twins are that:. For now, we are focusing on twins as a possible reason for the uterus being larger than expected. Here are two ways to try to hear the heartbeats of twins:. Because twin births are often more difficult or dangerous than single births, it is safer for the woman to go to a hospital to give birth.
Since twins are more likely to be born early, the mother should try to have transportation ready at all times after the 6th month. If the hospital is far away, the mother may wish to move closer in the last months of pregnancy. Be sure to have a plan for how to get help in an emergency.
Refer the woman to a health centre if you suspect she may have diabetes. She had diabetes in a past pregnancy. One of her past babies was born very big more than 4 kilograms , or was ill or died at birth and no one knows why. She is fat. She is thirsty all the time. She has frequent itching and a bad smell coming from her vagina.
Show references Divon MY. Fetal growth restriction: Screening and diagnosis. Accessed Oct. Peter JR, et al. Symphysial fundal height SFH measurement in pregnancy for detecting abnormal fetal growth.
Cochrane Database of Systematic Reviews. American College of Obstetricians and Gynecologists. Practice Bulletin No. See also 2nd trimester pregnancy Fetal development 2nd trimester Pregnancy due date calculator Prenatal care: 2nd trimester visits Pregnancy exercises Pregnancy stretches. Mayo Clinic Press Check out these best-sellers and special offers on books and newsletters from Mayo Clinic.
Reprint Permissions A single copy of these materials may be reprinted for noncommercial personal use only. The pressure from your uterus may cause your navel to stick out, but your navel should return to normal after birth. Starting between 18 and 20 weeks your doctor will measure the distance from your pubic bone to the top of your uterus in centimeters. The top of your uterus is called the fundus, so the measurement is called the fundal height.
This number usually corresponds with the number of weeks pregnant you are, give or take two centimeters. For example, if you measure 32 centimeters then you should be about 32 weeks pregnant. If this is not your first pregnancy it is normal for this measurement to be a bit bigger. If your uterus is the size it should be during your prenatal visits , this is a sign everything is progressing well with your pregnancy.
If it is measuring too big or too small, it could mean your due date is off, some kind of pregnancy complication or additional testing may be required. During your third trimester, the uterus will finish growing and be the size of a watermelon. When you reach full term your uterus will extend from the pubic area to the bottom of your rib cage.
As you get ready to give birth your baby should drop lower into your pelvis. After birth, your uterus will gradually return to its pre-pregnancy size and position.
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