Lactation is a physiological state of hyperprolactinemia and associated amenorrhea. Despite the fact that exact mechanisms standing behind the hypothalamus–pituitary–ovarian axis during lactation are still not clear, a general overview of events leading to amenorrhea may be suggested. Suckling remains the most important stimulus maintaining suppressive effect on ovaries after pregnancy. Breastfeeding is accompanied by high levels of prolactin, which remain higher than normal until the frequency and duration of daily suckling decreases and allows normal menstrual function resumption. Hyperprolactinemia induces the suppression of hypothalamic Kiss1 neurons that directly control the pulsatile release of GnRH. Disruption in the pulsatile manner of GnRH secretion results in a strongly decreased frequency of corresponding LH pulses. Inadequate LH secretion and lack of pre-ovulatory surge inhibit the progression of the follicular phase of a menstrual cycle and result in anovulation and amenorrhea. The main consequences of lactational amenorrhea are connected with fertility issues and increased bone turnover. Provided the fulfillment of all the established conditions of its use, the lactational amenorrhea method (LAM) efficiently protects against pregnancy. Because of its accessibility and lack of additional associated costs, LAM might be especially beneficial in low-income, developing countries, where modern contraception is hard to obtain. Breastfeeding alone is not equal to the LAM method, and therefore, it is not enough to successfully protect against conception. That is why LAM promotion should primarily focus on conditions under which its use is safe and effective. More studies on larger study groups should be conducted to determine and confirm the impact of behavioral factors, like suckling parameters, on the LAM efficacy. Lactational bone loss is a physiologic mechanism that enables providing a sufficient amount of calcium to the newborn. Despite the decline in bone mass during breastfeeding, it rebuilds after weaning and is not associated with a postmenopausal decrease in BMD and osteoporosis risk. Therefore, it should be a matter of concern only for lactating women with additional risk factors or with low BMD before pregnancy. The review summarizes the effect that breastfeeding exerts on the hypothalamus–pituitary axis as well as fertility and bone turnover aspects of lactational amenorrhea. We discuss the possibility of the use of lactation as contraception, along with this method’s prevalence, efficacy, and influencing factors. We also review the literature on the topic of lactational bone loss: its mechanism, severity, and persistence throughout life.

Objectives: Premature ovarian insufficiency (POI) is associated with hypoestrogenism and an increased risk of metabolic disorders. In many clinics, a variety of insulin resistance (IR) tests are used during routine clinical assessments. To date, there is no clear opinion about which of these tests should be applied in women with premature ovarian insufficiency (POI). Therefore, our preliminarily aim was to compare the most frequently used insulin resistance indexes in the clinical assessment of a group of POI women and a control group. Material and methods: Our retrospective study included 98 women with karyotypically normal spontaneous POI aged 18–39 years and a control group of 78 healthy women. Each patient was given an oral glucose tolerance test (OGTT) to evaluate their insulin release and insulin resistance. In addition, each woman’s insulin resistance (IR) was evaluated us­ing the homeostasis model assessment for insulin resistance (HOMA-IR), the quantitative insulin sensitivity check index (QUICKI), the fasting glucose-to-insulin ratio (FGIR), and Matsuda and McAuley indexes. The two groups’ glucose levels were compared at 0, 60 and 120 min of the OGTT. Results: At 0 and 60 min of the OGTT, the insulin levels of the POI women were significantly higher than those of the control group. The number of women in whom IR was detected using the various kits was comparable between the two groups. Conlusions: In conclusion, only the OGTT evaluation revealed a significant difference in insulin concentrations between the two study groups. The indexes most commonly used to detect IR did not detect differences in IR between the POI women and the members of the healthy control group. QUICKI detected significantly more women with IR within both study groups than other tests did. Objectives: Premature ovarian insufficiency (POI) is associated with hypoestrogenism and an increased risk of metabolic disorders. In many clinics, a variety of insulin resistance (IR) tests are used during routine clinical assessments. To date, there is no clear opinion about which of these tests should be applied in women with premature ovarian insufficiency (POI). Therefore, our preliminarily aim was to compare the most frequently used insulin resistance indexes in the clinical assessment of a group of POI women and a control group. Material and methods: Our retrospective study included 98 women with karyotypically normal spontaneous POI aged 18–39 years and a control group of 78 healthy women. Each patient was given an oral glucose tolerance test (OGTT) to evaluate their insulin release and insulin resistance. In addition, each woman’s insulin resistance (IR) was evaluated us­ing the homeostasis model assessment for insulin resistance (HOMA-IR), the quantitative insulin sensitivity check index (QUICKI), the fasting glucose-to-insulin ratio (FGIR), and Matsuda and McAuley indexes. The two groups’ glucose levels were compared at 0, 60 and 120 min of the OGTT. Results: At 0 and 60 min of the OGTT, the insulin levels of the POI women were significantly higher than those of the control group. The number of women in whom IR was detected using the various kits was comparable between the two groups. Conlusions: In conclusion, only the OGTT evaluation revealed a significant difference in insulin concentrations between the two study groups. The indexes most commonly used to detect IR did not detect differences in IR between the POI women and the members of the healthy control group. QUICKI detected significantly more women with IR within both study groups than other tests did.