Fecundity and twinning. A study within the Danish National Birth Cohort

Trends in Dizygotic and Monozygotic Spontaneous Twin Births During the Period 2007-2017 in Lombardy, Northern Italy: A Population-Based Study

In this study, we analyzed the estimated frequency of monozygotic (MZ) and dizygotic (DZ) spontaneous twins in Lombardy during the period 2007-2017. This is a population-based study using the regional healthcare utilization databases of the Lombardy Region. The total number of spontaneous twin deliveries, in separate strata of like and unlike sex, was obtained. Moreover, estimates of DZ and MZ twin births were calculated using Weinberg's method. The standardized rates (SRs), adjusted for maternal age, of DZ and MZ twin births were computed according to calendar period. The twinning rates were calculated among strata of parity and maternal age. Finally, DZ:MZ ratio was calculated. Among the 734,278 spontaneous deliveries, 9176 (12.5 out of 1000 births) couples of twins were identified. In the three periods considered (i.e. 2007-2010, 2011-2014 and 2015-2017), no trend in the SRs of MZ twins was observed, respectively 0.41 (95% CI [0.40, 0.43]), 0.43 (95% CI [0.42, 0.45]) and 0.43 (95% CI[0.42, 0.45]). Differently, a slightly decreasing trend was observed in DZ twins SRs, respectively 0.87 (95% CI [0.84, 0.89]), 0.81 (95% CI [0.79, 0.83]), and 0.78 (95% CI [0.76, 0.80]). As concerns parity and maternal age, the rate of DZ twin births was consistently higher in nulliparae women aged 35 years or more. In our cohort, despite the increase of maternal age, a decline of spontaneous twin births emerged, especially due to the downward trend of DZ twins.

Fathering of dizygotic twins and risk of prostate cancer: nationwide, population-based case-control study

BACKGROUND

An association between male fertility and risk of prostate cancer has been suggested, possibly through lower androgen levels in subfertile men. We evaluated male fertility in relation to risk of prostate cancer by assessing the frequency of fathering of dizygotic twins, a marker of high fertility, among cases of prostate cancer and controls.

METHODS

We performed a case-control study in Prostate Cancer data Base Sweden (PCBaSe), a nationwide, population-based cohort. PCBaSe was linked to the Swedish twin register for information on zygosity for same-sex twins and to other nationwide health care registers and demographic databases for information on socioeconomic factors, comorbidity, and tumor characteristics for 96 301 prostate cancer cases and 378 583 matched controls. To account for the influence of in vitro fertilization on dizygotic twinning, analyses were restricted to men who had fathered children before 1991, when in vitro fertilization was still uncommon in Sweden.

RESULTS

1 112 cases and 4 538 controls had fathered dizygotic twins. Men with dizygotic twins had no increased risk of prostate cancer compared to fathers of singletons; neither for total prostate cancer odds ratio (OR) 0.95(95% CI 0.89-1.02), nor for any risk category, OR 0.97 (95% CI 0.84-1.12) for low-risk disease, and OR 1.04 (95% CI 0.90-1.22) for metastatic disease.

CONCLUSION

The lack of association between fathering of dizygotic twins and prostate cancer risk give no support for an association between male fertility and prostate cancer risk.

Twins and Their Health Cost: Consequences of Multiple Births on Parental Health and Mortality in Denmark and England and Wales

The rapid increase in twinning rates in developed countries has increased interest in the question as to whether twin mothers have higher mortality and more health problems than mothers of singletons. Here we use a national survey, the Office for National Statistics Longitudinal Study of England & Wales, and a linkage between the Danish Twin Registry and the Danish population register to examine mortality patterns after age 45 (50 for fathers) for twin parents and the whole population born from 1911 to 1950. For England and Wales, presence of limiting long-term illnesses and self-rated health status was also investigated. Overall similar health and mortality was found for twin parents and the whole population although both life table methods and survival analysis suggested a slight excess mortality among older cohorts of twin mothers in England and Wales.

Chilean School-Age Children Twin Registry: Planning, Sampling and Implications

We describe subject recruitment from the University of Chile School-Age Children Twin Registry (REMEUCHI). The research aim of REMEUCHI is to quantify the impact of genetic and environmental factors on scholastic achievement in a multicausal approach. The Ministry of Education of Chile, in collaboration with the Registry Office, provided the list of possible twin pairs graduated from high school in 2004 in Chile's metropolitan region. From a population of 70,065 school-age children who had graduated from high school, 434 possible twin pairs were analyzed. Of these, 327 were twins reared together (75.3% of the 434 possible twins pairs) and born between 1986 and 1987 in Chile (mean age 18 years), and approximately 8% were not twins despite matches on full name and birth data. The rest of the possible twin pairs were probably twins reared apart, since one member of the pair had moved to study in another region of Chile. Zygosity was determined through questionnaires, maternal reports of twin similarities, and by the hospital records of the twins at the time of birth. Three hundred and twenty-seven pairs were identified, where monozygotic (MZ) and dizygotic (DZ) twins represented 46.8% and 53.2% of pairs, respectively, with a DZ/MZ ratio of 1.14. Considering same-sex MZ pairs, the percentage of female pairs was greater (55.6%) than male pairs (44.4%). When DZ pairs were analyzed, 47.7% were of opposite sex, 20.1% were male pairs and 32.2% female pairs. In Chile, these findings represent a baseline study to contribute to the establishment of a national twin registry in the future.

Twinning Rates According to Maternal Birthweight

Dizygotic twinning rates have changed over time, which has been seen as a sign of a decline in fecundity. Since a woman's birthweight has been shown to be a marker of her fecundity, maternal birthweight may correlate with subsequent twinning rates. In the Danish National Birth Cohort (1996–2002), we examined if maternal birthweight, and whether she was born at term or preterm, correlated with her probability of multiple birth. For 20,719 live born infants, we had self-reported information about maternal birthweight, collected during the first wave of the 7-year follow-up, and information on multiple births from record linkage. The association between maternal birthweight and multiple births was investigated by use of logistic regression and presented as odds ratios (ORs) with 95% confidence intervals (CIs). Compared to women born at term with a birthweight of 3001–4000 g, women with a birthweight > 4500 g appeared to have higher chance of multiple birth while women with a birthweight of 4001–4500 had a lower chance, especially if the analysis was restricted to women with a BMI < 25 (Adjusted ORs 2.3 [1.0–5.4] and 0.4 [0.2–0.9] respectively). Odds ratios for dizygotic twinning were of the same magnitude. In women with a BMI ≥ 25, no obvious pattern was present. Our findings do not indicate that twinning is a fecundity indicator. Women with a birthweight that may indicate a pregnancy complicated with gestational diabetes had the highest rate of multiple birth. These findings are new and should be put to a critical test in other data sources.

Twinning in the offspring of parents with chronic radiation exposure from nuclear testing in Kazakhstan

The population of the Semipalatinsk region of Kazakhstan was chronically exposed to radioactive fallout from above-ground nuclear tests conducted during 1949-1956 by the Soviet Union. We investigated the effect of radiation exposure and other factors on risks of twinning overall and of same- and different-sex twinning and hence estimated dizygotic and monozygotic twinning rates in 11,605 deliveries around Semipalatinsk, 141 of which were twin, to 3992 mothers exposed to fallout during 1949-1956. Overall, the same-sex twinning rate was 7.85 [95% confidence interval (CI): 6.24, 9.47] per 1000 and the opposite-sex twinning rate was 4.45 (95% CI: 3.23, 5.67). Twinning rates did not differ significantly between radiation exposure categories, parental age at main radiation exposure, or year of birth. Different-sex, but not same-sex, twinning increased with maternal age (P(trend) = 0.04) but not with other demographic factors and was increased soon after radiation exposure [OR = 4.08 (95% CI: 1.11, 15.07)] for births occurring within 5 years compared with more than 20 years after exposure; this effect was similar in villages with low and high radiation exposure, however, so interpretation is uncertain.

Trends in the probability of twins and males in California, 1983-2003

This study examines the probability of twins by birth year, maternal race-ethnicity, age, and parity and the influences of these demographic factors on the probability of male in twins and singletons in a large, racially diverse population. Recent publications note steep increases in twin births while the probability of male births has been reported to vary by parental race-ethnicity and age and birth order. Probability of male stratified by plurality has not been investigated in California prior to this study. Cubic spline estimates and Poisson regression techniques were employed to describe trends in twins and males using California vital statistics birth and fetal death records over the period from 1983-2003. This study includes 127,787 twin pair and 11,025,106 singleton births. The probability of twins varied by birth year, maternal race-ethnicity, age, and parity. The probability of twins increased by 10.1% from 1983-1992 and increased by 20.1% from 1993-2003, nearly doubling the previous increase. All maternal race-ethnicity groups showed increases in probability of twins with increasing maternal age. Parous women compared to nulliparous women had larger increases in the probability of twins. The probability of males in twins decreased from 1983-1992 and increased from 1993-2003; while in singletons the probability appeared unchanged. These findings show increases in the probability of twins in California from 1983-2003 and identify maternal age, race-ethnicity, and parity groups most likely to conceive twins. The cause of the increase in twins is unknown but coincides with trends towards delayed childbearing and increased use of subfertility treatments.

Subfertility among parents of men diagnosed with testicular cancer

It is well known that men with testicular cancer also have reduced fertility before diagnosis. It is unclear, however, whether their parents also have reduced fertility. We performed a population-based record linkage study comparing parental fertility among 3711 testicular cancer cases and 371 100 control males. The cases were diagnosed from 1961 to 2001, and the data were analysed by logistic regression. Included indicators of parental fertility were number of children, rate of unlike-sex twins as a proxy for dizygotic twinning rate, and proportion of boys. The number of children was reduced across increasing sibship size among both mothers [odds ratio (OR) = 0.95, p(trend) = 0.003] and fathers [OR = 0.97, p(trend) = 0.057] of subjects with testicular cancer. The proportion of unlike-sex twins was also reduced among their mothers [(OR = 0.56, p = 0.049 (adjusted for year of birth)] and fathers [(OR = 0.56, p = 0.049 (adjusted for year of birth)]. The results were only marginally changed when also adjusting for respective parental age. Our study indicates that parents of testicular cancer cases have reduced fertility. This suggests that genetic factors are important in the association between testicular cancer and reduced fertility.

Genetic and environmental risk factors for testicular cancer

Germ-cell testicular cancer has a well-characterized descriptive epidemiology, whereas the aetiology remains largely unknown. It is believed that exposures acting prenatally are instrumental to germ-cell cancer development, although no specific exposure has been identified. Several epidemiological studies have investigated a number of indicators of prenatal exposures, such as birth order, gestational duration, birth weight, maternal age and nausea during pregnancy, but results are inconsistent. This paper briefly reviews the current support for genetic and environmental factors in testicular cancer aetiology. In particular, we have summarized the evidence suggesting a strong role of inherited susceptibility, which is probably carried by the effect of several unknown moderate-risk genes. We have illustrated inconsistencies in the previous studies on prenatal factors by estimating the heterogeneity and pooled odds ratios among twelve studies investigating the association between low birth weight and testicular cancer. We have discussed the possibility that puberty is another time window during which environmental factors may increase the risk of testicular cancer. Finally, we have reviewed the results from studies on cryptorchidism and impaired fertility in relation to risk for testicular cancer. In conclusion, we propose that future aetiological studies on testicular cancer should take postnatal exposures acting during puberty into account and, whenever possible, investigate both main effects and interactions among prenatal factors, genetic factors and postnatal factors.

Infertility, infertility treatment and twinning: the Danish National Birth Cohort

BACKGROUND

We have previously observed that an increasing time to pregnancy (TTP) is associated with a reduced frequency of twin deliveries in couples not receiving infertility treatment. By using updated information, we assessed the frequencies of dizygotic (DZ) and monozygotic (MZ) twin deliveries as a function of infertility (TTP > 12 months), as well as infertility treatment.

METHODS

From the Danish National Birth Cohort (1997-2003), we identified 51 730 fertile couples with TTP <or= 12 months, 5838 infertile couples who conceived naturally with TTP > 12 months and 5163 infertile couples who conceived after treatment. Information on zygosity, available for part of the cohort (1997-2000), was based on standardized questions on the similarities between the twins at the age of 3-5 years.

RESULTS

Compared with fertile couples, the frequency of DZ twin deliveries was lower for infertile couples conceiving naturally (odds ratio 0.4, 95% confidence interval 0.2-0.7) and was much higher for infertile couples conceiving after treatment (17.3, 14.4-20.7). The frequency of DZ twin deliveries decreased with TTP in untreated couples, whereas the frequency of MZ twin deliveries remained constant.

CONCLUSIONS

The frequency of DZ twin deliveries decreased with TTP and substantially increased with infertility treatment, whereas MZ twin deliveries remained substantially unchanged.

Twin pregnancy possibly associated with high semen quality

BACKGROUND

Recent studies found an association between a long waiting time to pregnancy (TTP) and reduced probability of twinning and a reduced dizygotic (DZ) twinning rate in subfertile men. However, it remains unsolved whether semen quality is associated with twin offspring. We therefore studied the semen quality in a group of fathers of naturally conceived twins.

METHODS

In this study, 37 fathers of DZ twins and 15 fathers of monozygotic (MZ) twins participated, and 349 normal fertile men served as a reference group. All men delivered a semen sample, underwent a physical examination and completed a questionnaire.

RESULTS

After adjustment, fathers of DZ and MZ twins had 3.6 (95% CI 1.7; 5.4) and 4.6 (95% CI 2.0; 7.2) percentage points higher percentage of sperm cells with normal morphologic features and percentages of motile sperm cells were 11.5 (95% CI 7.2; 15.9) and 12.5 (95% CI 6.3; 18.6) percentage points higher than the reference group (P < 0.01). Fathers of DZ twins and MZ twins had 24.7 (95% CI; -9.1; 71.3) and 17.0% (-25.2%; 83.0%) higher sperm concentration than the reference group.

CONCLUSIONS

Fathers of DZ twins had a better semen quality than the reference group, which supports the assumption that spontaneous DZ twinning rate can be used as a sensor of male fecundity of a population.

Time to pregnancy and multiple births

BACKGROUND

Mothers of multiples are alleged to be more fecund than mothers of singletons. Some authors have suggested monitoring twinning rates for assessing temporal changes in a population's reproductive health.

METHODS

Using a nested case-control design, we estimated the odds of a multiple birth in relation to fecundity in the US Collaborative Perinatal Project inclusive of 8546 pregnant women who reported a known time-to-pregnancy (TTP) upon enrolment in the cohort, 1959-1966. Case mothers comprised 81 women giving birth to twins/triplets; control mothers comprised 243 women giving birth to singletons matched to case mothers on maternal age at a ratio of 3:1. The odds ratio (OR) for a multiple birth within 6 months of trying adjusting for maternal age and prior pregnancies was estimated using logistic regression. Discrete time Cox regression analysis was also utilized to estimate the fecundability OR.

RESULTS

Women with a TTP of <or=6 months were more likely to have a multiple birth than women reporting a TTP of >6 months [OR=1.95; 95% confidence interval (95% CI)=1.09-3.51]. Excluding pregnancies after 13+ months resulted in a loss of precision (OR=2.14; 95% CI=0.90-5.04).

CONCLUSIONS

These data support higher fecundity among mothers of multiples than mothers of singletons.

Time to pregnancy and pregnancy outcome

OBJECTIVE

To investigate whether the outcome of a pregnancy is related to the time required to achieve that pregnancy (TTP).

DESIGN

The distribution of the TTP for pregnancies ending in multiple birth, early (before week 12) and late (weeks 12-28) miscarriage, stillbirth, and extrauterine pregnancy was compared to that of pregnancies ending in singleton birth. Furthermore, the distribution of the TTP for preterm singleton births was compared to that of full-term singleton births.

SETTING

Sweden.

PATIENT(S)

Information from three previous studies on reproduction was used: Women chosen for exposure to persistent organochlorine pollutants, or exposure as a hairdresser, and their respective controls.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Self-reported pregnancy outcome.

RESULT(S)

An increased TTP (i.e., decreased fecundability) was associated with pregnancies ending in miscarriage (early as well as late) and extrauterine pregnancies. Pregnancies ending in multiple live birth tended to have shorter TTPs than those ending in single live birth. No association between TTP and stillbirths was found. Among women whose pregnancies ended in singleton birth, a prolonged TTP was associated with preterm delivery.

CONCLUSION(S)

The TTP of a pregnancy seemed to be associated with the outcome of that pregnancy. The mechanisms behind this phenomenon are, however, unclear.

Fertility Among Brothers of Patients with Testicular Cancer

OBJECTIVE

Patients with testicular cancer have decreased fertility prior to the diagnosis of cancer, although it is not clear whether the subfertility is the result of an emerging tumor, or whether subfertility and testicular cancer share causes. To test if they share causes, we assessed fertility among brothers of patients with testicular cancer.

METHODS

We compared 5,613 siblings (2,878 brothers) of patients with germ-cell testicular cancer, diagnosed in Sweden from 1960 to 2002, with 6,151 population controls (3,202 men). Using the Swedish Multi-Generation Register, we obtained information on the number of children born (until December 2003) from cases (n = 9,480) and controls (n = 10,739). Fertility was measured using two indicators, (a) offspring twinning rates, as dizygotic twinning is reduced by male subfertility, and (b) number of children. We used unconditional logistic regression, and analyzed brothers and sisters separately. Analyses on the number of children were restricted to subjects (39%) born prior to 1954, for whom information on reproductive life until age 50 was available.

RESULTS

Brothers, but not sisters, of patients with testicular cancer were less likely to have unlike-sex twins than controls (for unlike-sex twins, the odds ratio for the father being a sibling of testicular cancer patient was 0.53; 95% confidence interval, 0.26-1.09). The likelihood of being a brother of a patient with testicular cancer decreased monotonically with increasing number of children (P = 0.05), whereas no association was observed for the sisters.

CONCLUSION

The decreased fertility found among brothers of patients with testicular cancer argues in favor of shared causes between cancer-associated subfertility and testicular cancer. Genetic links and shared environment could explain the association.