**3. Reproduction treatment and advanced maternal age**

#### **3.1. Low ovarian reserve**

The effect of age in the ovarian reserve is unavoidable. Although menopause is considered the end of the reproductive age in women, changes in the ovarian cycle take place many years prior to menopause. These changes may lead to a fertility dysfunction in women that decide to get pregnant at an advanced age. The primary mechanism behind this process is the decrease of primordial follicle count in the ovary susceptible to developing a good-quality ovule. Classically, follicle count during menstrual cycle has been assessed using ultrasound. In addition, numerous studies have reported changes in the hormone patterns associated with reproductive ageing, such as shortened follicular phase, elevated follicular phase oestrogen, and decreased luteal phase progesterone [8–13]. During the last decade, anti-Müllerian hormone (AMH) has emerged as an early biochemical marker able to predict the decrease in the ovarian reserve. Low AMH serum levels predict an altered folliculogenesis by inhibiting the recruitment of primordial follicles and its sensitivity to FSH [14]. The reduction of AMH serum levels appears to be more strongly and more consistently correlated with age than the decrease number of antral follicles observed in the ovary by ultrasound, inhibin B levels, or FSH levels [15, 16].

with a risk of miscarriage *per se* of 0.35% (CI 95%: 0.07 to 0.63) following amniocentesis and

Multiple Pregnancy in Women of Advanced Reproductive Age

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The use of donor oocytes in assisted reproduction techniques (ARTs) during the last decades has been a great advance for women whose reproductive dysfunction could not be treated otherwise. It was initially addressed for young women with premature ovarian failure. But this technique provides a valuable weapon to avoid age-related changes in the ovary, allowing premenopausal and menopausal women to get pregnant and fulfil their reproductive desire with acceptable success rates [28–30]. Moreover, the use of oocytes from donors has numerous advantages, as it reduces the rate of aneuploidies and stillbirth in women of advanced age. Case reports of successful pregnancy and delivery in a 70-year-old patient with donated oocytes demonstrate that the uterus may be able to maintain pregnancy far beyond the age of menopause [21]. Women are delaying childbearing; it is likely that the percentage of women looking for donor oocytes will increase, as it has been in the last

Twins occur spontaneously, and we still do not understand the causes or the conditions under which an embryo decides to split in two. However, the vast majority of twin pregnancies, particularly in women of advanced reproductive age, happened as a result of ART. Women seeking reproductive treatment usually have been trying to conceive spontaneously for a long period of time, and many have undergone previous unsuccessful treatments. Frustration, impatience, and economic costs are probably the main reasons why transfer of two and even three embryos is still a common practice in many countries [1]. This practice increases the chances of achieving pregnancy per embryo-transfer but also increases the chances of obtaining a multiple pregnancy. Multiple pregnancies have an important impact on the mothers' and babies' health as a consequence of medical and obstetric complications, and this carries an important economic burden for society, mainly due to preterm delivery, long hospital stay of the premature babies, and treatment of subsequent disabilities

For obvious reasons, the main strategy to reduce the number of twin pregnancies in all women is the widespread use of the single embryo transfer (sET) during a fertility treatment. Our target should be to resemble the spontaneous twinning rate of embryos. Thanks to the development of vitrification, a fast freezing technique that increases post-thawed embryo survival rate, a single embryo can be transferred in a fresh cycle, while the rest will be transferred posteriorly in vitrified-thawed cycles without any loss of implantation potential [32]. The latest studies show the promising potential of sET to markedly reduce the risk of multiple pregnancy without affecting pregnancy outcomes. Even though sET might increase the time to pregnancy, minimising the risk of twin pregnancy becomes a huge advantage for public

0.35% (95% CI: -0.31 to 1.00) following chorionic villus sampling [27].

**3.5. Strategies to reduce twin pregnancies in the elderly mother**

and individual health, particularly for elderly mothers.

**3.4. Oocyte donation**

decade.

in the long term [31].
