By Mom Loves Best. Reviewed by Michelle Roth, BA, IBLCLC

Many myths persist about how breastfeeding, fertility, and ovulation are connected. As we go throughout this guide, we will take a closer look at how your hormones continue to change as you breastfeed and how these changes affect your fertility. We’ll also examine what you can do to either start or stop your chances of becoming pregnant during this period of time.

Your Menstrual Cycle

A woman’s ovary releases an egg during the ovulation period, which travels into the fallopian tube to await fertilization. The womb becomes thick with a lining to house the egg. If sperm fertilizes the egg and it successfully implants in the uterus, you become pregnant.

If the egg is not fertilized, the womb sheds its lining and menstruation begins.

Knowing What’s Normal For You

While every woman is different, the typical menstrual cycle lasts for 28 days ⁽²⁾. The best way to understand your own cycle is to track it.

Tracking includes marking down the days you have your period, bodily changes (such as charting temperature and cervical mucus changes), personal symptoms (such as cramping and moodiness), and signs of ovulation ⁽³⁾.

How Your Cycle Changes After Pregnancy

During pregnancy, the menstrual cycle completely stops as your little one grows and develops. After pregnancy, the reemergence of your menstrual cycle will be largely determined by breastfeeding.

Why is this? The hormone necessary for breast milk production suppresses ovulation ⁽⁴⁾.

Take Note:  A woman who exclusively breastfeeds may not experience a menstrual cycle until she stops breastfeeding. A woman who does not breastfeed at all can generally expect her first menstrual cycle to occur between six and eight weeks after giving birth ⁽⁵⁾.

For all other mothers who breastfeed but supplement with formula or who have older babies trying out new foods in addition to breast milk, the timing of the first menstrual cycle will vary.

Understanding Your Breastfeeding Hormones

During pregnancy and throughout your postpartum experience, you will experience many hormonal fluctuations. While you may feel these changes were simply designed to drive you crazy, they have a very real effect on your body’s ability to take care of your baby.

The hormones we will discuss include:

• Prolactin.
• Estrogen.
• Progesterone.
• Oxytocin.

Your body uses the hormone prolactin to produce breast milk. The very name of this hormone comes from its importance to lactation ⁽⁶⁾. Prolactin is also the mothering hormone – creating those protective feelings you have toward your baby.

Prolactin is produced in the pituitary gland and begins secreting into your body eight weeks into pregnancy. The levels slowly rise, peaking at birth.

However, your body also produces high levels of estrogen and progesterone, which are known as the “pregnancy hormones.” These prevent the high levels of prolactin from causing your milk to be produced and flow right out throughout your pregnancy.

At birth, the pregnancy hormones drop dramatically, allowing the prolactin to fully activate and breast milk to start flowing ⁽⁷⁾. It is at this stage oxytocin begins to be produced. While oxytocin was the main hormone of birth – contracting your uterus and helping your baby into the world – its role changes now for breastfeeding.

Also created in the pituitary gland, oxytocin’s primary role is to deliver the milk prolactin has signal to be produced. Milk will be released from the milk-making glands when oxytocin signals to the breast that more milk needs to come out.

All of these hormones work together to ensure both your pregnancy and your breastfeeding experience goes smoothly.

How Prolactin Affects Fertility

Of all these hormones, prolactin is the one that has the most direct impact on your fertility.

Ovulation occurs when gonadotropin-releasing hormone signals to another hormone, follicle stimulating hormone, to release an egg for fertilization and to prepare the womb to house it ⁽⁸⁾.

Prolactin suppresses both of these hormones, effectively stopping ovulation, the key step in the menstrual cycle for reproduction. This is why so many women are able to use breastfeeding as a natural form of birth control.

In fact, less than 1 out of 100 women will become pregnant in the first six months when exclusively breastfeeding ⁽⁹⁾.

Birth Control and Breastfeeding

While it is clear breastfeeding is an effective form of birth control, experts urge women to remember two things:

1. Exclusive breastfeeding, sometimes referred to as continuous breastfeeding, is the key to prolactin’s success in suppressing ovulation. This means you only give your baby breast milk without any other liquids, including water. Pumping also makes breastfeeding less effective as a form of birth control.
2. Breastfeeding is temporary as a birth control method and can only be relied upon for six months at the most. At the six-month mark, you will likely begin introducing other foods into your baby’s diet.

If your goal is to prevent pregnancy, you should be very careful when using breastfeeding as a form of birth control. Because ovulation occurs before menstruation, you will not know if you are experiencing a fertile period before your period returns.

The best way to ensure breastfeeding works is to exclusively breastfeed and use a back-up form of birth control if you can answer yes to any of these questions:

• Is your baby older than 6 months?
• Has your period returned?
• Are you supplementing breastfeeding with bottles of formula or pumped milk, or has your baby started solids?

Pro Tip: If you are pumping, it is necessary to pump on a frequent schedule that mimics breastfeeding. One of the reasons pumping is not as effective as nursing as a birth control method is because pumping is often too infrequent, signaling your body to lessen prolactin production

STAY TUNED FOR PART 2 to learn about exclusive breastfeeding, fertility signs while breastfeeding, and how to improve fertility.