Ultrasound-determined due dates are most accurate during the first trimester, and measuring 'ahead' doesn't result in a changed due date in most cases.
Some reasons the fetus may measure ahead or large for gestational age are: Your due date is wrong. You have uterine fibroids. You have a BMI of over 25 (have overweight or obesity). You are carrying twins or triplets.
Your doctor does not have to induce your labor early if you're carrying a large baby. Early induction of labor doesn't necessarily prevent complications or birth injuries. However, your doctor might want to get your labor started if you are a week or two past your due date.
The researchers found that precise prediction is basically impossible. Regardless of which method they used to determine estimated Date of Birth, the actual Date of Birth showed considerable variation between babies (up to 2 weeks before, and 2 weeks after).
They suggest that the due date should only be changed after a third trimester pregnancy ultrasound if 1) it is the pregnant person's first ultrasound, and 2) it is more than 21 days different than the due date suggested by the LMP (ACOG, 2017).
Your baby's size will be monitored as the pregnancy continues. You may be scanned to see if you have extra fluid around the baby and/or tested for gestational diabetes to see why the baby may be measuring ahead. However usually there is no need to intervene.
Your fundal height is above average.
It could be that your uterus size doesn't sync up with the standard growth charts (i.e. you measure big). And if the measurements are off by three weeks or more, in many cases your due date is moved to reflect this.
In general, this doesn't happen a lot—but it usually depends on how your due date is calculated in the first place. “If dating is only based on the last menstrual period and a later ultrasound shows a discrepancy, then the due date may be changed,” Lamppa says.
Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.
A premature birth is more likely to happen when a mother has a health problem — like diabetes — or does harmful things during her pregnancy, like smoke or drink. If she lives with a lot of stress, that also can make her baby be born too early. Many things can cause a baby to be born early or with health problems.
Before we break down the evidence, here are some of the common reasons your OB or midwife may cite when suggesting an early induction (before 40 weeks) for a suspected large baby. A large baby's shoulders may get stuck (shoulder dystocia) while being born.
Vaginal birth is still recommended is your baby is estimated to weigh less than 5,000 g (10 lbs) if you don't have diabetes. If your baby is estimated to weigh more than 4,500 g (8.4 lbs), and your labor stalls in the active stage or the baby doesn't descend, this is an indication for cesarean delivery.
Although excessive weight gain during pregnancy is sometimes linked to larger birth weights, a bigger baby bump doesn't always mean a big baby. It's hard to ignore or not be bothered by comments about how "huge" you're getting. (On the flip side, many women also catch flak for not looking pregnant enough.)
More than 90% are born two weeks either side of the predicted date. But, as noted above, only 4% (or 4.4%, ignoring pregnancies with complications etc) are born on the predicted date itself - in other words, the chance of this happening is less than one in 20.
An ultrasound is actually the most accurate way to date a pregnancy because all fetuses grow at a consistent rate during the first trimester and early second.
This is because pregnancy is counted from the first day of the woman's last period, not the date of conception which generally occurs 2 weeks later, followed by 5 to 7 days before it settles in the uterus.
If you have any of these signs or symptoms before your 37th week of pregnancy, you may be experiencing preterm labor: Change in your vaginal discharge (watery, mucus or bloody) or more vaginal discharge than usual. Pressure in your pelvis or lower belly, like your baby is pushing down. Constant low, dull backache.
About 60 out of 100 women give birth on or before their given due date. In another 35 out of 100 women, contractions start on their own within two weeks of the due date. But it takes longer in about 5 out of 100 women.
First-trimester ultrasound (ultrasound before 13 weeks and 6/7 days) is the most accurate method to establish or confirm gestation age in pregnancy[1]. First-trimester ultrasound can be performed either trans-vaginally or trans-abdominally.
Evidence suggests that ultrasounds more accurately predict your due date than using your last menstrual period—but only in the first trimester and early second trimester (until roughly 20 weeks). 3 Early ultrasound due dates have a margin of error of roughly 1.2 weeks.
If your menstrual cycle is longer, this means you ovulated later in your cycle and that your estimated due date will be later. If your menstrual period is shorter, this means that you ovulated earlier in your cycle and that your estimated due date will be earlier.
Most of the time, there's a harmless explanation. Maybe your due date is off by a few days or a week (it's pretty common for doctors to change due dates). Your baby could be in a funny position or sitting high in your uterus, and that's throwing the tape measure off.
It is common for each ultrasound throughout pregnancy to predict a different due date. Earlier ultrasounds are more accurate in terms of predicting the due date, so that's why doctors will usually use the dates and measurements from the first ultrasound of the pregnancy as a reference.
Summary. From early in your pregnancy it is best to keep in mind that due dates are only a guide. Only about five per cent of women give birth on the exact date they are due. Most babies arrive between 37 weeks and 41 weeks of pregnancy, but usually within a week either side of their expected due date.
Generally, only the smallest 3 percent truly have growth restriction, typically measuring 2-3 weeks behind. In extreme cases, babies may measure 4-8 weeks behind.