**3. Impact of multiple gestations**

Source: CDC/NCHS, National Vital Statistics System [6]

eries of 22 per 1000 [10].

204 Contemporary Gynecologic Practice

a genetic founder effect [14].

**Figure 1.** Twin birth rates, by age of mother. United States, 1980 and 2009.

fertility drugs and treatments, genetics and others [4, 5, 12].

A consistent growth in the number of multiple births in England has also been well docu‐ mented [7]. Analysis from the North of England Multiple Pregnancy Register during 1998 and 2002 showed an increasing twinning rate of 13.6 to 16.6 per 1, 000 maternities [8]. Similarly, secular changes in twinning rates were demonstrated by previous study, in which 15 out of 17 European countries listed significant increasing proportions between 1972 and 1996 [9]. Records from the Danish National Birth Cohort revealed an overall frequency of twin deliv‐

Over the last 20 years in Japan, the incidence of twin births increased until 2003, when it started to decrease reaching similar rates to those registered in the 1990s [11]. The reported Chinese twinning rates range from 2.8 to 15.4 per 1000 births. This wide variation may be explained by the lack of systematic vital records [12]. Historically, the lowest twinning rates are registered in Asian countries (5-6 per 1000 maternities), and the highest rates are seen in Sub-Saharan-Africa (23 per 1000 maternities), notably Nigeria, with rates up to 40 per 1000 births [13].

The average rate of twin births in Brazil is 10 per 1000. Cândido Godói is a modest town in South Brazil universally known as "Twins' Town", considering its twinning rate of 2% and an estimated rate of 10% in the very small district of Linha São Pedro. It was hypothesized that such a high rate of twin births could be due to Nazi's experiments commanded by Joseph Mengele in the 1960s. Recent data suggest that this phenomenon is much better explained by

There is a global tendency of an increased number of multiple gestations, with the exception of triplets and higher-order multiple gestations [15]. This fact was largely attributed to an elevated amount of dizygotic pregnancies, without significant variations in monozygotic births over the past few decades [4]. The dizygotic twinning rate is affected by innumerous factors such as race, parental consanguinity, maternal age and parity, lifestyle, season, use of Multiple pregnancies are strongly associated with greater maternal morbidity. Studies demonstrate a maternal mortality risk as much as three times higher and the numbers of intensive care unit admissions are nearly twice as those in singleton [16]. Major obstetrics complications include: miscarriage, growth retardation, pre-eclampsia, gestational diabetes, caesarean section, preterm delivery and post-partum hemorrhage [17].

Multiple children are at increased lifetime risk of developing medical complications, mainly due to the extremely high rate of preterm delivery and low birth weight among twins. Of all factors contributing to perinatal mortality, preterm newborns alone account for 70%. Likewise, infants born with less than 2500g are almost 40 times more likely to die during early infancy [18, 19]. Population-based data show greater proportions of disabilities in twins compared to singleton, with up to 3 to 7-fold increase in cerebral palsy [5, 20]. Furthermore, twinning phenomenon is associated with a higher incidence of congenital anomalies, especially among monozygotic pregnancies [16, 20].

Becoming pregnant of more than one baby imposes supplementary social implications during the antenatal and the postnatal periods. Most parents exhibit feelings of shock and isolation, which may often lead to psychological consequences such as postnatal depression. Moreover, women carrying multiples are more likely to suffer with the severity of pregnancy symptoms. Also, myths and misunderstandings regarding multiples generate many issues that the maternity care provider should be prepared to explain. Lack of sleep and personal time, chronic stress, fatigue, exhaustion and financial strains are common dilemmas experienced by parents. Delayed development, attention deficit and learning difficulties usually affect multiple children, especially due to lack of sufficient one-to-one stimulation. The prevalence of disabilities is estimated to be at least 50% higher in twins and 100% in triplets [17, 20].

In addition to all negative consequences of multiples, economic implications should also be considered. The increase in multiple births defies the current trend to lower medical costs [19]. A large study conducted in the Brigham and Women's Hospital by Callahan et al. [21] showed that multiple pregnancies contribute to a dramatic rise in hospital charges. Total family charges for a 29-year-old white mother in 1991 was estimated to be US\$ 9, 845 for a singleton, compared to US\$ 37, 947 for a mother of twins and US\$ 109, 765 for higher-order multiple-gestation [21]. In large scale it could trigger a public health collapse.
