Have you ever heard of Naegele’s rule?

Most pregnancy due dates are calculated using France Naegele’s (a German obstetrician from 1851) rule of thumb, his rule will add seven days and nine months to the first day of your last menstrual period. (LMP) You can also use an ultrasound to decipher your special birthday via charting babies measurements.

Factors Affecting Due Dates:

• Menstrual Cycle Variability: As mentioned, not all women have a 28-day menstrual cycle. Variations in cycle length can affect the calculation of the due date.
• Conception Date: Accurately pinpointing the date of conception can be challenging, especially for couples who are not actively tracking their fertility.
• Individual Pregnancy Variation: Every pregnancy is unique, and factors such as the rate of fetal growth can vary from person to person.
• Inaccurate LMP Tracking: Some individuals may have difficulty recalling the exact date of their last menstrual period, leading to potential inaccuracies in due date calculation.

A study from Finland, with 17 000 people, found that an ultrasound from anywhere between 8-16 weeks was more accurate than using your last menstrual period. 

Having a ‘one size fits all’ due date calculator just doesn’t work. As it assumes that all women’s cycles are the same. The reality is that we ovulate at different times, our cycles can be a little longer or shorter etc. (Evidence Based Birth)

Only 5% of babies arrive on their “due date.” Accuracy of ultrasounds past 20 weeks tend to be less accurate(AIMS)

The Risks of Being 'Overdue': It's essential to understand that due dates are not hard deadlines. According to data from the Perinatal Institute, only 4% of people give birth on their estimated date. Many factors can contribute to a pregnancy continuing beyond the estimated due date. While post-term pregnancies are relatively common, healthcare providers typically monitor them closely to assess the health of both the baby and the mother. Potential risks associated with being overdue include:

• Reduced Amniotic Fluid: As the pregnancy progresses, there may be a reduction in amniotic fluid, which can impact fetal well-being.
• Placental Function: The placenta may begin to deteriorate with time, affecting the baby's oxygen and nutrient supply.
• Increased Risk of Interventions: Prolonged pregnancies may lead to medical interventions such as induction of labour or caesarean section.

Due dates can vary based on your genetics, ethnicity, whether it's your first or second baby, time between when you ovulated and the egg was implanted, higher weight gain in pregnancy, stress levels - to name a few. Due dates are valuable reference points in pregnancy, but they are not definitive predictions. Remember, every pregnancy is unique, and the focus should always be on the health and well-being of both the mother and the baby, rather than solely on the calendar date. As a doula, I encourage open communication with healthcare providers and the exploration of all available options for a safe and positive birth experience.