Due Date FAQ
1. How is my pregnancy due date calculated?
The medical term for “due date” is EDD, or estimated date of delivery — which means the date your practitioner gives you is only an educated estimate. Your due date is usually calculated this way : Subtract three months from the first day of your last menstrual period (LMP), then add seven days — that’s your due date the following year. For example, say your last period began on April 11. Count backward three months, which gets you to January, and then add seven days. Your pregnancy due date would be January 18.
2. How many babies are born on their due dates?
According to most studies, only one in 20 babies is actually born on his or her due date. Because a normal pregnancy often lasts anywhere from 38 to 42 weeks, most infants are born within two weeks either way of your EDD — which keeps most parents guessing right to delivery day.
3. Why does this dating system sometimes not work?
This pregnancy system works well for women who have a regularly menstrual cycle. But if your cycle is irregular, the system may not work for you at all. Say you typically get your period every six to seven weeks and haven’t had one in three months. On testing, you find out you’re pregnant. When did you conceive? Because a reliable EDD is important, you and your practitioner will have to try to come up with one. But even if you can’t pinpoint when you conceived or aren’t sure when you last ovulated, other clues can help you to determine your due date.
4. How else is my due date calculated?
There are a few additional clues that will help your practitioner determine your EDD and confirm your stage of pregnancy:
- The size of your uterus, which will be noted when your initial internal pregnancy examination is performed.
- An early ultrasound, which can more accurately date the pregnancy (however note that not all women get an early ultrasound — some practitioners perform them routinely, but others only recommend one if your periods are irregular, if you have a history of miscarriages or pregnancy complications, or if the EDD can’t be determined based on your LMP and physical exam).
- Pregnancy milestones such as the first time a fetal heartbeat is heard (at about 9 weeks to 12 weeks of pregnancy) as well as when you first feel fetal movement (at about 16 weeks to 22 weeks), can give clues to whether your EDD is accurate.
- Your fundal height, or the top of your uterus, is measured by your practitioner at each prenatal visit; the fundus should reach your navel at about week 20, which helps confirm your EDD.
5. Can my due date change?
Yes, your due date can change. While it’s certainly no cause for concern, your doctor may change your due date for a number of reasons as your pregnancy progresses, including if your periods are irregular and your initial ultrasound dating was off, if your first ultrasound was in the second trimester, if you have an abnormal fundal height, or if you have abnormal AFP levels.
6. When should I first see the doctor?
Good prenatal care is one of the most important ingredients in making a healthy baby. So don’t delay. As soon as you suspect you might be pregnant or have a positive home pregnancy test, call your practitioner to schedule your first prenatal appointment.
7. What tests should I expect at my first doctor appointment?
You can expect a number of screenings and tests at your first prenatal appointment to confirm your due dateand check up on your health and your baby’s, including a urine test, Rh factor test, initial blood workup, and your old friend the Pap smear. They may seem tedious, but they help ensure a healthier pregnancy and delivery.