The average human pregnancy is 40 weeks long. However, a pregnancy is considered term between 37 weeks and 41 weeks 6 days. Babies born on or before 36 weeks 6 days are consider preterm or premature. Babies born between 37 weeks and 38 weeks 6 days are considered early term. Babies born between 39 weeks and 40 weeks 6 days are considered full term. Babies born between 41 weeks and 41 weeks 6 days. Babies born on or after 42 weeks are consider post-term or post-date. (Note: Prior to October 2013, babies were considered term between week 37 and week 42 of gestation.)
To calculate the length of your pregnancy, begin with the date of ovulation. The two weeks prior to ovulation are considered weeks 1 and 2 of pregnancy. For women who ovulate on day 14 of the menstrual cycle, day 1 of pregnancy will correspond with day 1 of the last menstrual period (LMP).
Pregnancy can be divided into days, weeks, months, and trimesters. Day 1 marks the beginning of week 1, month 1, and the first trimester. A baby is conceived during week 3, and day 15 marks the beginning of week 3. The average pregnancy is 280 days long.
Another way to discuss the days and weeks of pregnancy is to combine the two units of measurement. Week 1 of pregnancy begins at 0 weeks 1 day and ends at 1 week 0 days of pregnancy. Week 2 encompasses the time between 1 week 1 day and 2 weeks 0 days of pregnancy. A baby born at 38 weeks 3 days of pregnancy is born during week 39 of pregnancy.
Although most health care providers will take about the length of pregnancy in terms of weeks, the weeks of pregnancy can also be combined into months. Because some months are longer than others, some months consists of 4 weeks while others consist of 5 weeks. The average pregnancy is 9 months long. (Click on the calendar to view the full size of the image.)
Pregnancy can also be broken down into trimesters. The first three months of pregnancy comprise the first trimester. Months 4, 5, and 6 comprise the second trimester. The third trimester consists of months 7, 8, and 9 of pregnancy.
In addition to the days of pregnancy, the length of a pregnancy can also be determined by calculating the days post ovulation (DPO). Day 15 of pregnancy is also 1 DPO. The average pregnancy lasts 266 DPO.
References
Ob-Gyns Redefine Meaning of “Term Pregnancy”: http://www.acog.org/About-ACOG/News-Room/News-Releases/2013/Ob-Gyns-Redefine-Meaning-of-Term-Pregnancy
Pregnancy Length: http://www.baby2see.com/pregnancylength.html
Image Credits
Weeks and Days of Pregnancy © 2012 Heather Johnson
Weeks, Months, and Trimesters of Pregnancy © 2012 Heather Johnson
Month 1 of Pregnancy © 2012 Heather Johnson
Month 2 of Pregnancy © 2012 Heather Johnson
Month 3 of Pregnancy © 2012 Heather Johnson
Month 4 of Pregnancy © 2012 Heather Johnson
Month 5 of Pregnancy © 2012 Heather Johnson
Month 6 of Pregnancy © 2012 Heather Johnson
Month 7 of Pregnancy © 2012 Heather Johnson
Month 8 of Pregnancy © 2012 Heather Johnson
Month 9 of Pregnancy © 2012 Heather Johnson
Month 10 of Pregnancy © 2012 Heather Johnson
