Reena is a new age, smart, educated, working professional. She is particular about everything, from her dress… to her make- up… to her exercise schedule ….to her career plan. She wants to plan the childbirth well. Right from maternity photoshoot to shopping. She wants to have her bag packed and go fully prepared when “the time” comes! Being her Obstetrician, I have already calculated her EDD ( expected due date) but every sonography report gives her a different due date!! So she just wants to know the answer to the million-dollar question:
Will I deliver on the due date?
So let me give one-line answer:
And the answer is a BIG NO.
Even if the due date is calculated by the most reliable method, only 5 % babies arrive on the due date!

Expected due date is an important but a very rough calculation!!!!!

Why is due date important?
Doctors refer to the expected due date all the time. Once the doctor calculates the age of a pregnancy (gestational age), the doctor can check if the pregnancy is growing appropriately. According to the stage of pregnancy the doctor advises specific tests.
When does the baby come out?
Almost 80% of women deliver within the two weeks before the due date [ between 38-40 weeks]. Very few, around 7% women go beyond the due date.
All babies born within a span of three weeks before the due date ( 37-40 weeks) are called “Full term”. The baby gets fully mature three weeks before the due date.
Few women cross over the due date. In such cases, one has to be cautious about the health of the baby.
How is the due date calculated?
The baby stays in the womb roughly for around 266 days. Studies have shown that Asians and black people have a slightly short pregnancy as compared to white.
No one can surely predict the exact date when the egg got fertilised (Exception: IVF procedure). So the calculation is backtracked to the first day of last menstrual period by adding 14 days( 266+14= 280 days). Thus we add 280 days or 40 weeks to the first day of the last menstrual period to predict the expected due date.
This formula works only if you have when a woman has a regular menstrual cycle of 28 days. More the irregularity in cycles more inaccurate the calculation is.

Is due date calculated by sonography more accurate?
The sonography machine calculates the age of pregnancy based on the size of the baby and predicts the due date. Due date calculated by sonography is little more reliable than from Last menstrual period. The due date calculated by sonography done in the first three months is more reliable than sonographies done in later pregnancy. In cases of IVF pregnancy, one can be most sure of the due date.
Yet, despite meticulous calculations, only 5% of babies will come out on the exact day.
Should one calculate month-wise or week-wise?
Both mean the same thing. Many find it very confusing to do these calculations. The reason is simple. Except for the month of February, all other months have 30/31 days. This means that a typical month is of four weeks and 2/3 days extra to it. If we add up these 2/3 extra days over three months span, one can say that three months almost becomes 13 weeks and not 12 weeks. Thus six months equal to 26 weeks and nine months equal to 39 weeks.
In conclusion:
• Expected due date is a rough estimation.
• Most women deliver between 38-40 weeks
• Babies born after 37 weeks are full term babies
• No one can surely predict the day when the baby will be born. So watch for signs of labour especially when you are in last 15 days and be ready for “the day”.