**3.4. Oocyte donation**

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].

In addition to changes observed in the ovarian reserve and quality of the oocytes, the uterus is an essential organ to achieve pregnancy. As in any other human organ, ageing also has an effect on the uterus of fertile women. Even though it is difficult to evaluate these changes in humans, animal studies indicate that older mice show an impaired artificially induced decidual response, probably due to reduced progesterone secretion [17–19]. Microscopic changes have also been confirmed, with more hyperaemia and higher vascular development and growth of the myometrium and stroma of young hamsters in comparison with the older ones [20]. Older mothers are also more likely to experience intrapartum complications and the rate of caesarean delivery is higher, suggesting that myometrial function is impaired by advanced maternal age [21]. The risk of stillbirth in mothers over the age of 40 is twice as high as younger mothers due to foetal chromosomal abnormalities, multiple pregnancy, obesity, pre-eclampsia, insulin-dependent diabetes, and multiple pregnancy [21, 22]. These evidences suggest that changes in the uterus in older women may have a reflection on fertility and the

Women who delay childbearing are at an increased risk of foetal chromosomal abnormalities. This occurs as a consequence of an error in chromosomal disjunction during maternal meiosis I or II, which has been reported as more frequent in advanced age women [23–25]. Among them, numeric chromosomal abnormalities seem to be more frequent than structural chromosomal abnormalities. Chromosomal aneuploidies related to maternal age include trisomy 21, trisomy 18, trisomy 13, triple X syndrome, and Klinefelter syndrome [26]. A recent study highlights that trisomy 21 showed an incidence rate of 11.34 out of 1000 cases at the age of 35 years, 15.41 cases at the age of 40, and 37.04 cases at the age of 45. In addition, trisomy 18 showed an incidence rate of 1.89 out of 1000 cases at the age of 35 years, 5.14 cases at the age of 40, and 37.04 cases at the age of 45. Nowadays, prenatal diagnostic techniques such as ultrasound and cell-free foetal DNA test allow professionals to make an early screening for foetal aneuploidy. However, invasive techniques remain the gold standard for definitive diagnosis,

**3.2. Ageing uterus**

102 Multiple Pregnancy - New Challenges

ability of maintaining a pregnancy.

**3.3. Chromosomal abnormalities**

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 decade.

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

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 in the long term [31].

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 and individual health, particularly for elderly mothers.
