Monitor the health of your community here

How to Tell the Size of Your Unborn Baby

Few things are more exciting than following the development of your unborn baby when you have found out you're pregnant. Despite the advanced technology of the 21st century, your baby, beginning as just about the size of a tip on a pen, and growing to a 7 to 8 lb. baby who can sustain life outside the womb in only 40 weeks, is still a wonder of nature. There are several ways for you to tell the size of your baby and follow how he changes, week to week. This may connect you to your baby emotionally and help you to feel a greater part of the life inside you.

Calculate your due date. The most common method used to calculate when your baby is due is to figure out the first day of your last menstrual period. If you're planning to get pregnant, this will be easier to keep track of. Though your doctor will use the first day of your last period, you are considered two weeks along at the time of conception. A typical pregnancy is 40 weeks or 280 days in length.

How to Measure Baby Weight by Ultrasound

Learn More

Buy a book, or check one out at your library, about the development of your baby week by week or month by month. Your choices are plentiful. Many of these books have vivid descriptions and actual photographs of what your baby looks like and is going through at any given time 1. Though conception usually occurs on days 11 through 21 of your cycle, sperm can live up to four days in cervical mucous before it meets with the egg.

Check out the internet. There are many options to choose from when you use your search engine to find "Unborn baby development, week by week," or something similar. Use a source you can trust such as an established medical site or obstetrics site. There you will find descriptions and vivid pictures explaining your baby's size and development. Then you may forward that information to family and friends and have them follow along with you each month.

Accuracy of Transvaginal Ultrasound for Dating Pregnancy

Learn More

Call for an appointment with an obstetrician when you are about eight weeks along. This is when your doctor may want to perform your first ultrasound to document your baby's size and gestational age. According to, fetal measurements are most accurate in early pregnancy, about 7 to 13 weeks. Measurement testing includes Crown to Rump, which is from the crown of the head to the base of baby's bottom. This is a "very accurate" way to measure fetal size. Other measurements taken include the biparietal diameter, which is the diameter between the two sides of baby's head, taken after 13 weeks; the femur length test, which gauges the length of the longest bone in the body, the femur of the leg. To measure size in late pregnancy, states "the abdominal circumference is the single most important measurement to tell fetal size and weight, rather than age."