What laboratory tests should be ordered for a 28-year-old female presenting with secondary amenorrhea (absence of menstruation) for 3 months, with a history of pregnancy at 27 years of age, suspected to be experiencing lactational amenorrhea (amenorrhea due to breastfeeding)?

From the Guidelines

The most appropriate initial laboratory test for a 28-year-old female presenting with secondary amenorrhea and suspected lactational amenorrhea is prolactin. In this clinical scenario, the patient's recent history of pregnancy and breastfeeding suggests that lactational amenorrhea may be the cause of her secondary amenorrhea. Lactational amenorrhea occurs because breastfeeding stimulates prolactin secretion, which suppresses gonadotropin-releasing hormone (GnRH) and subsequently inhibits ovulation, as noted in a study published in the Annual Review of Clinical Psychology 1. Elevated prolactin levels are expected during breastfeeding and can cause amenorrhea for several months postpartum, temporarily suppressing the hypothalamic-pituitary-ovarian axis. While other hormones such as FSH and estrogen may also be affected during this period, the primary hormone responsible for lactational amenorrhea is prolactin, making it the most relevant parameter to assess in this clinical scenario, as also suggested by guidelines from the American College of Obstetricians and Gynecologists (ACOG) 1. Some key points to consider when evaluating this patient include:

• The patient's medical history, including her recent pregnancy and breastfeeding status
• A physical examination to rule out any other potential causes of amenorrhea
• Selected laboratory tests, including prolactin levels, to confirm the diagnosis of lactational amenorrhea
• Consideration of other potential causes of anovulation, such as hyperandrogenic conditions, hypothalamic dysfunction, thyroid disease, and primary pituitary disease, if prolactin levels are not elevated. Checking prolactin levels would help confirm whether the patient's amenorrhea is due to lactation or if another cause should be investigated.

From the Research

Laboratory Tests for Secondary Amenorrhea

To determine the underlying cause of secondary amenorrhea in a 28-year-old female with a history of pregnancy and suspected lactational amenorrhea, the following laboratory tests should be ordered:

• Pregnancy test to rule out pregnancy as the cause of amenorrhea 2, 3
• Serum levels of:
  • Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to evaluate ovarian function 2, 3
  • Prolactin to check for hyperprolactinemia, a common cause of amenorrhea 2, 3
  • Thyroid-stimulating hormone (TSH) to assess thyroid function, as thyroid disorders can cause amenorrhea 2, 3
• If serum prolactin and TSH levels are normal, a progesterone challenge test may be performed to determine outflow tract patency and estrogen status 3
• If the patient is found to have hypoestrogenic amenorrhea, serum gonadotropin levels may be measured to determine whether amenorrhea represents ovarian failure or pituitary or hypothalamic dysfunction 3

Considerations for Lactational Amenorrhea

In the case of suspected lactational amenorrhea, it is essential to note that:

• Lactational amenorrhea can provide excellent contraceptive protection for up to 6 months post-partum, irrespective of when supplements are introduced into the baby's diet 4, 5
• The lactational amenorrhea method (LAM) can be relied on for good contraceptive protection for up to 12 months post-partum in women who continue to breastfeed 5
• However, once menstruation has returned, other forms of contraception are essential to prevent pregnancy 5