Thanks Cassandra for this great question. This is really important to understand when considering LAM or the Lactational Amenorrhea Method of birth control.
Typically you ovulate 14 days before your period starts. But when you are exclusively or intensively breastfeeding--pumping as frequently as you would normally breastfeed, the opposite is true. The following is from the Academy of Breastfeeding Medicine's Protocol Contraception During Breastfeeding:
Amenorrhea is the most important [aspect]..., as it alone is associated with a significant reduction in fertility. The intensity of the breastfeeding is also very important since it contributes both to the duration of amenorrhea and to the suppression of normal ovulation in the first postpartum cycle, creating the physiological conditions to ensure that the first bleed will tend to precede the first adequate ovulatory development.
- LAM is 98-99% effective in preventing pregnancy during the first six months.
- In Rwanda, the method was used the first nine months, continuing breastfeeding frequency by feeding before each solid foods feeding.
- Women pumping after return to work, as long as they pumped with the same frequency as the baby normally feeds, had a 96.5% efficacy rate using LAM.
Read more about breastfeeding and birth control