How are due dates calculated?
The standard calculation is called Nägele’s Rule. This was developed in the 1850’s by a Dr. Nägele, who determined that the average human pregnancy was 266 days from conception, or 280 days (40 weeks) from the start of the last menstrual period. To calculate this, begin with the first day of your last period (LMP). Add 7 days, then subtract 3 months.
((LMP + 7 days) – 3 months) = Expected Date of Delivery
EX: ((April 1 + 7 days) – 3 months) = January 8
This “rule” doesn’t take into account the fact that many women are uncertain of the date of their last menstrual period, not all women have 28 day cycles, and not all women ovulate on day 14 of their cycle.
Another Calculation
In 1990, researchers (Mittendorf, et al) re-examined this issue for modern American women. Results indicated that, for first-time Caucasian moms, an average pregnancy lasts 274 days from conception (approximately 288 days from the last menstrual period).
This research and other studies also show us many other factors influence the length of pregnancy, including: mother’s age, weight, ethnicity, prenatal care, prenatal nutrition and smoking, number of prior pregnancies, and more.
Mittendorf shows an average pregnancy is 269 days for mothers who’ve given birth before. Non-Caucasian moms have shorter pregnancies than Caucasian moms; for example, African-American women average 266 days.
So, to calculate “Mittendorf’s Rule”. Begin with the starting date of the last menstrual period. Add 15 days for first time Caucasian mom, or add 10 days if you’re non-white or this is not your first baby. Then subtract 3 months.
((LMP + 15 days) – 3 months) = Expected Date of Delivery
EX: ((April 1 + 15 days) – 3 months) = January 16
What other methods can tell what the gestational age is / how many weeks pregnant someone is?
Those calculations predict a due date based on the date of conception. If the date of conception and the date of the last menstrual period are unknown, there are several other ways to determine how far along the pregnancy is.
- Ultrasound: Ultrasound can be used to examine the baby’s development, and determine his/her age based on which systems are fully developed. If ultrasound is performed in the first trimester, it can indicate fetal age within a range of 3 – 5 days. Later in pregnancy, it is less accurate. Up to 20 weeks, the margin of error is 7 – 10 days. By the third trimester, an ultrasound date can be off by as much as 3 weeks in either direction. Therefore, a baby that appears “term” (40 weeks) may be anywhere from 37 – 43 weeks.
- Heart Tones: Fetal heartbeat can be heard through Doppler starting at 9-12 weeks and by stethoscope at 18-20 weeks.
- Fundal height: A physician or midwife can measure mom’s belly, specifically the distance from the symphisis pubis joint to her fundus (the top of her uterus). Fundal height can indicate the size of the baby, which can give insight about fetal age. Typically, from week 24 to week 34, fundal height in centimeters correlates with weeks of gestation. For example, at 28 weeks, the fundus is probably about 28 cm. This is not an exact measurement, and several factors can affect its accuracy.
- Quickening: Some believe the baby will come five months after quickening, the first time the mother feels the baby move. This is hard to evaluate, as women can be more or less sensitive to these sensations, and may notice them at different times in their pregnancies. (First time mothers typically notice movement around 18-20 weeks. Mothers who have been pregnant before notice it as early as 16 weeks.)
Even if you know your exact date of conception, and the exact gestational age of your baby, and know the “average” length of pregnancy, it is still difficult to predict exactly when your baby will be born. A normal pregnancy can last anywhere from 37 to 42 weeks. Only 4% of babies are actually born on their “due dates”. 6-10% of babies are born early – prior to 37 weeks; 4-14% of pregnancies last more then 42 weeks.
So, when will your baby be born?
If this leaves you very confused, just realize that predicting due dates is a very inexact science. Make sure you have everything ready for your baby and for your birth by two weeks before your due date. But then have some really fun and exciting projects to keep you busy for up to two weeks after your due date, that way you don’t feel too frustrated if your baby comes a little later than “expected.”
Incoming search terms for the article:Pregnancy Due Date Calculator pregnancy calculation pregnancy due date due date calculation average length pregnancy first time moms due date calculator pregnant can a conception date be off by 3 weeks in the first trimester fetal age calculator due date average length of first pregnancy pregnancy ultrasound third trimester gestational Age normal pregnancy average length of gestation for first time mom first time moms due date accuracy pregnancy information for first time mothers average pregnancy length first time mothers average length of pregnancy in caucasians medicare for babies pregnancy due time pregnancy time calculation if my due date is on 6th april when 37 weeks fall on 8th or 9 months is the baby comes out exact the calculation? mittendorf calculation medicare rules for mom and baby margin of error on conception dates margin of error in pregnancy date margin of error conception ultrasound margin calculation medicines live pregnancy delivery last menstrual period example calculation problems mittendorf rule if i get pregnate in may what is a due date how many weeks pregnancy am i how many weeks ar you if you due date is may 24 how many days before due date delivery is normal how far along is my pregnancy calculator how far along is my pregnancy how far along am i in my pregnancy calculator how far a long is my pregnancy how can i measure expected date of delivery of baby how to calculate due date ethnicity age how to calculate due date from the date of conception how many babies are born with medicare ia skippping recommended at the time of 1st month of pregnancy http://medicare in/womens-health/pregnancy-due-date-calculation/ how to tell conception date through due date how to calculate the fundal height six months gestation How to calculate pregnancy if last periods date is unknown how to calculate pregnancy if last menstrual period is unknown how to calculate fetal age if ia 8 weeks pregnate what is my due date mittendorfs rule modern pregnancy due date calculation pregnancy with unknown LMP pregnency due date stages of human pregnancy-EDD calculator Third time mom due date third trimester fundal belly length cm week chart third trimester ultrasound medicare ultrasound due dates 3 weeks off ultrasound in 9 week pregnancy UNKNOWN LMP BUT HAVE DUE DATE what is my due date based on fetal age when LMP is unknown? what is the average length of pregnancy for first time moms? What is the average length of pregnancy for first time mothers? what is the average week first pregnancy babies are born what is the date of conception with period date expected pregnancy at home women pregnancy period calculte pregnancy weeks calculator taking into account the length of menstrual cycle pregnancy symptoms 6 weeks pregnant pregnancy month calculator My Fundal height is 24 how far along am I? naegeles rule 1st time moms normal pregnancy BEFORE EDD NORMAL PREGNANCY DELIVERY ON DUE DATE predicting babys birth based on date of first movement predicting due date how far along am i pregnancy 16 weeks 3 days from lmp pregnancy baby care pregnancy calculation off by 4 weeks pregnancy calculator and due date pregnancy delivery calculation pregnancy due accuracy pregnancy due date calculation pregnancy due date ultrasound pregnancy due date with unknown last period pregnancy length first time mom wordpress blogs gestational age of 3 weeks 3 days pregnancy symptoms 10 weeks pregnancy average lenghth of time for a human pregnancy average length of fundus in pregnancy 40 weeks average length of pregnancy for african-americans average length of pregnancy for first time moms average pregnancy due date average pregnancy due date white average pregnancy length first time mom average pregnecy first time baby born in how many weeks baby due calculation baby due date and conception date baby due date calculation calculate due date of delivery calculate your due date calculating gestational age by ultrasound calculation of weeks in pregnancy calculation of weeks of pregnancy average gestation of first time mom average gestation for first baby 14 weeks pregnancy 1st pregnancy is prior to the date or latter 1st time mothers and due dates 288 days of pregnancy 3 weeks pregnancy symptoms 37 weeks pregnancy 37 weeks pregnant and homeopathy 8th month of pregnancy mothers weight accuracy of pregnancy calculation accuracy of pregnancy due date first time mom african american women due date african american women have shorter pregnancies Are Due date calculations accurate average date on which first time caucasian mothers deliver average due dates first pregnancy average gestation first caucasian pregnancy average gestation for a first time mom can conception be 10 days off by ultrasound can first time moms have their baby at 37 weeks? can i be off in my due date calculations by a month due dates 3 months duedatecalculation error pregnancy due date expected date of delivery indicates how many weeks expected due date calculation factores influencing pregnancy due date accuracy fetal age calculation first time mom making due date first time moms and due date accurate first time moms average length of pregnancy first time pregnancy average week of delivery first time pregnancy length first trimester ultrasound foetal length calculator for gestational age fundal height at 16 weeks fundal height third trimester error in conception date gestation calculator unknown lmp due date mittendorf due date for first time moms CAN I BELIEVE ON MY LAST MENSTRUAL PERIOD THAT CAME UP IN THE ULTRASOUND EVEN IF I AM SURE IT WAS BEFORE THAT DATE can pregnancy be expected before due date? conception based on due date conception calculator conception date conception date accuracy conception date based on how far along i am conception date with unknown lmp determine conception lmp unknown determining fetal sex at 24 weeks doppler measurements & calculations of a 20 weeks baby due date 2 methods 1st time mom due date based on height and ethnicity due date calculations due date calculator if period date unknown due date calculator unknown period date due date conception date quickening gestational age & height of uterus