“Measure what is measurable, and make measurable what is not so” (Galileo Galilei)

What's math got to do with it with getting pregnant and pregnancy? This deals with all aspects of pregnancy.

  • From counting minutes, hours, days, weeks, and years.
  • Measuring the fetus and other parts of the pregnancy.
  • To understand what's normal in terms of numbers and what's not.

Mathematics is the science that deals with numbers. It is all around us, in everything we do, and it plays a significant role in getting pregnant and pregnancy, making a baby to having one.

This page on babyMed is dedicated to the mathematics of pregnancy and fertility, bringing together the numbers aspects related to reproductive health.


z=days after ovulation.
EXAMPLE: 9dpo=9 days after ovulation


x=amount of days after a y-day embryo transfer. For IVF pregnancies.
EXAMPLE:7dp5dt= days after a 5-day embryo transfer.  In general, if you add X (dp or days after transfer)  and y (embryo transfer day) the you have about dpo.  
EXAMPLE: x=7 and y=5, the sum is 12 which is about 12 dpo.

How are these numbers related to pregnancy 

1: The number of fetuses in a singleton pregnancy
2: The number of fetuses in a twin pregnancy
2: The number of vessels in a two-vessel cord
3: The number of fetuses in a triplet pregnancy
3: The number of vessels in the normal umbilical cord
4-5: The average number of days of a menstrual period
5-6: The number of fertile days in a menstrual cycle
5-6: The number of days a sperm can survive inside the uterus
9: The average days between fertilization and implantation
9.98: The perinatal mortality rate per 1,000 live births in the first 28 days of life in 2013 in the United States
10: "Count to 10" How many time the fetus should move within a certain time frame
13: Weeks when the 2nd trimester begins

14: The day when in a 28-day menstrual cycle ovulation happens

18-20: The weeks when an anatomy sonogram is usually done
21: The minimum number of days in a normal menstrual cycle
22-24: The weeks when a fetus becomes viable
5-25: The blood level mIU/ml of HCG human chorionic gonadotropin to determine that there is a pregnancy
25-29.9: The BMI or body mass index when someone is considered overweight
27: Weeks when the third trimester begins
28: The maternal mortality rate per 100,000 births in 2013 in the United States
28: The days of an average menstrual cycle
30: The BMI or body mass index when obesity begins
35: The maximum number of days in a menstrual cycle

37-39: The weeks of an early term pregnancy
39-41: The weeks a term pregnancy 
41-42: The weeks a late-term pregnancy 
42+: The weeks a post-term pregnancy begins

120: The lowest normal fetal heart rate
160: The highest normal fetal heart rate
266: Or 38 weeks. The number of days between fertilization/ovulation and the calculated due date
280: Or 40 weeks. The number of days from the 1st day of the menstrual period (if it's 2 weeks before ovulation) until the due date
400: The average number of eggs (out of 1-2 Million at birth) that will mature over a woman's fertile life (age 15-45 or so)
500: The weight of the fetus in grams above which it is generally considered viable

2,000: Generally the number of grams below which a baby gets admitted to the NICU
4,000: The baby weight in grams (or 4,500) above which it's usually considered to be "macrosomic" (big).
400,000: The number of immature eggs a girl has at the time of menarche (when ovulation and the menstrual cycle begin)
1-2 Million: The number of immature eggs a girl has at birth
3.7 Million: About how many babies are born each year in the United States (as of 2020)
10 Million: The number of sperms in the ejaculate the make you less fertile
100 Million: The average number of sperm in a normal ejaculate