Table of ContentsView AllTable of ContentsGestational AgeHow to CalculateEstimated Due Date
Table of ContentsView All
View All
Table of Contents
Gestational Age
How to Calculate
Estimated Due Date
Learn about gestational age, how to calculate it, tracking pregnancy, and more.
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When people ask, “How far along are you?,” most people respond with the gestational age. The gestational age is the number of days andweeks of pregnancybeginning on the first day of the last menstrual period. Gestational age measures the age of gestation (pregnancy), not the age of thefetus.
Conception occurs during (and shortly after) ovulation, a time frame known as thefertility window. For people with a 28-day cycle, ovulation occurs approximately two weeks after the first day of the last menstrual period.
Experts use a 28-day cycle to calculate gestational age based on the average menstrual cycle length. However, a “normal” cycle lasts anywhere from 23 to 35 days, and not all menstruating people fall within that range.People generally on a 28-day cycle can experience occasional changes and may ovulate early or late.
Since gestational age is based on the date of your last period—and not the date of conception—you are considered four weeks pregnant at the time of your first missed period.
How to Calculate Gestational Age
When calculating the gestational age, the first day of your last menstrual period is considered day one. After that, it is generally counted in weeks plus the number of days past the previous week. For example, the gestational age could be 16 weeks and three days, meaning three days past 16 weeks.
Use this date as an estimate only, especially if you have not been tracking your menstrual period. The first day of the last menstrual period is accurately remembered and used only about half the time.
Tracking Estimated Delivery Date With Gestational Age
How Gestational Age Is Used During Pregnancy and After Birth
Healthcare providers use gestational age to measure pregnancy progress and monitor for potential complications. It is referenced regularly throughout pregnancy.
Babies born before 37 weeks of gestation are considered premature, which happens in up to 16% of pregnancies.Babies born prematurely may hit milestones later than full-term babies in the first year of life and sometimes beyond.
Summary
While the estimated delivery date is 40 weeks gestation, that estimate is not always accurate. The menstrual cycle length can vary, conception can happen on different days throughout the cycle, and babies may be born early or late for various reasons. Providers may use gestational age to assess the developmental milestones of babies born before 37 weeks gestation.
6 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.Gestational age.National Health Service.Periods and fertility in the menstrual cycle.UpToDate.Calculator: Estimated date of delivery (EDD) (Patient education).American Congress of Obstetricians and Gynecologists.Methods for estimating the due date.Grieger JA, Norman RJ.Menstrual cycle length and patterns in a global cohort of women using a mobile phone app: retrospective cohort study.J Med Internet Res. 2020;22(6):e17109. doi:10.2196/17109World Health Organization.Preterm birth.
6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.Gestational age.National Health Service.Periods and fertility in the menstrual cycle.UpToDate.Calculator: Estimated date of delivery (EDD) (Patient education).American Congress of Obstetricians and Gynecologists.Methods for estimating the due date.Grieger JA, Norman RJ.Menstrual cycle length and patterns in a global cohort of women using a mobile phone app: retrospective cohort study.J Med Internet Res. 2020;22(6):e17109. doi:10.2196/17109World Health Organization.Preterm birth.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
MedlinePlus.Gestational age.National Health Service.Periods and fertility in the menstrual cycle.UpToDate.Calculator: Estimated date of delivery (EDD) (Patient education).American Congress of Obstetricians and Gynecologists.Methods for estimating the due date.Grieger JA, Norman RJ.Menstrual cycle length and patterns in a global cohort of women using a mobile phone app: retrospective cohort study.J Med Internet Res. 2020;22(6):e17109. doi:10.2196/17109World Health Organization.Preterm birth.
MedlinePlus.Gestational age.
National Health Service.Periods and fertility in the menstrual cycle.
UpToDate.Calculator: Estimated date of delivery (EDD) (Patient education).
American Congress of Obstetricians and Gynecologists.Methods for estimating the due date.
Grieger JA, Norman RJ.Menstrual cycle length and patterns in a global cohort of women using a mobile phone app: retrospective cohort study.J Med Internet Res. 2020;22(6):e17109. doi:10.2196/17109
World Health Organization.Preterm birth.
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