Background: Offspring sex ratio (OSR) serves as an important social factor, and various other factors are hypothesized to be associated with it, such as maternal diet, time of ovulation and insemination, environmental phenomena, parental age, and infertility treatment. Objectives: This research was performed to assess the association between mothersâ�� menarche age, first pregnancy age, and sex ratio of first offspring. Patients and Methods: In this retrospective study, 2,000 Iranian women of reproductive age were recruited to assess their menarche age, first pregnancy age, and first OSR. Results: The mean age of the participants was 29.6 Â± 7.09, their mean menarche age was 13.25 Â± 1.21, and the mean age of their first pregnancy was 23.9 Â± 4.35. Total OSR was 0.932. The OSR (calculated as the proportion of male to female offspring) was higher when the menarche age was younger (P < 0.05). In women of younger pregnancy age, the OSR was higher (P < 0.05). First pregnancy age was younger in women with a menarche age under 13 years (P < 0.05). Conclusions: Women of younger menarche age will have younger first pregnancy ages and a greater chance of having a male first offspring. Â© 2016, Shiraz University of Medical Sciences

Barzegar, N.

Haghighi, L.

Hashemi, N.

Moradi, Y.

Najmi, Z.

eprints Iran University of Medical Sciences

Shiraz E-Med J. 2016 January; 17(1):e37365.Published online 2016 January 30.doi: 10.17795/semj37365.Research ArticleThe Association Between Menarche Age and First Offspring Sex RatioLadan Haghighi,1 Neda Hashemi,2 Yousef Moradi,3 Niloofar Barzegar,1 and Zahra Najmi2,*1Iran University of Medical Sciences, Tehran, IR Iran2Endometriosis Research Center, Iran University of Medical Sciences, Tehran, IR Iran3Pars Advanced and Minimally Invasive Manners Research Center, Pars Hospital, Iran University of Medical Sciences, Tehran, IR Iran*Corresponding author: Zahra Najmi, Endometriosis Research Center, Iran University of Medical Sciences, Tehran, IR Iran. Tel/Fax: +98-2166517342, E-mail: zahranaj@yahoo.comReceived 2015 November 30; Accepted 2016 January 09.AbstractBackground: Offspring sex ratio (OSR) serves as an important social factor, and various other factors are hypothesized to be asso-ciated with it, such as maternal diet, time of ovulation and insemination, environmental phenomena, parental age, and infertilitytreatment.Objectives: This research was performed to assess the association between mothers’ menarche age, first pregnancy age, and sexratio of first offspring.Patients and Methods: In this retrospective study, 2,000 Iranian women of reproductive age were recruited to assess their menar-che age, first pregnancy age, and first OSR.Results: The mean age of the participants was 29.6± 7.09, their mean menarche age was 13.25± 1.21, and the mean age of their firstpregnancy was 23.9± 4.35. Total OSR was 0.932. The OSR (calculated as the proportion of male to female offspring) was higher whenthe menarche age was younger (P < 0.05). In women of younger pregnancy age, the OSR was higher (P < 0.05). First pregnancy agewas younger in women with a menarche age under 13 years (P < 0.05).Conclusions: Women of younger menarche age will have younger first pregnancy ages and a greater chance of having a male firstoffspring.Keywords: Menarche Age, First Offspring Sex Ratio, First Pregnancy Age, Iran1. BackgroundThe age of the onset of menarche is affected by variousfactors, the most important of which have proven to be nu-tritional and health status, quality of life, socioeconomicstatus, and body size (1-3). There are also a number of oth-ers that include genetic, racial and geographic factors (4,5) and maternal or paternal factors, such as the mother’smenarche age, maternal age at the child’s birth, parents’smoking during pregnancy, etc. (6, 7). Girls with bettersocioeconomic status and higher body mass index (BMI)seem to have earlier menarche, which is hypothesized tobe associated to hormone mediators (8, 9). These factorsmake the mean menarche age variable in different soci-eties.Offspring gender is an important ecological issue in so-cieties, as it may influence the family size (10), parents’ be-havior and care, and governmental strategies (11).The offspring sex ratio (OSR) is reported to be variablein different societies and in different eras. Fukuda has re-ported a male to female sex ratio of 1.04 in Japanese societyin 2002 and 2011 (12, 13). But, some countries have reporteddecreasing or increasing OSR during recent decades (14,15). The latest studies of OSR in Iran were obtained in2002 and reported an OSR of 0.52 in 1976, which decreasedslightly in 2000 due to the Iran-Iraq War (16). However, norecent studies are available on the OSR of the Iranian pop-ulation.Studies have associated many factors to offspring gen-der, such as birth order, paternal age, digit length ratio(17, 18), parental hormone levels, drugs and toxins (19-21),maternal nutrition, physical and or mental health status(22, 23), time of intercourse, and infertility treatment (24,25). Although some factors are hypothesized to be asso-ciated with sex ratio, the mechanisms remain unclear, al-though Navara (23) has reviewed some possible mecha-nisms. Recent studies have associated mother’s menarcheage to child’s gender (13).In societies like Iran, where the gender of the child isof great importance for families and has a great impact onthe society, assessing the determinants of sex ratio is valu-able. Thus, we intended to assess the possible associationbetween mother’s menarche age and sex ratio of the off-spring, identifying the sex ratio of offspring, which has notyet been reported in Iran, as far as we know.Copyright © 2016, Shiraz University of Medical Sciences. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided theoriginal work is properly cited.Haghighi L et al.2. ObjectivesThis research was performed to assess the associationbetween mothers’ menarche age, first pregnancy age, andsex ratio of first offspring.3. Patients and MethodsThis study retrospectively assessed all Iranian womenof reproductive age who were referred from 2010 to 2014to Akbarabadi and Rasule Akram hospitals in Tehran, Iranand Kasra hospital in Karaj, Iran. Cases included womenwho had at least one child that was born after 20 weeks ofgestation. Patients with a history of infertility, endocrinedisorders, and polycystic ovarian syndrome and patientswho used assisted reproductive techniques for their firstpregnancy were excluded from analysis. From the 2,000women included in our study, demographic data, includ-ing mother’s age, parity, gravidity, menarche age, genderof children, and age at first delivery were collected. Theprotocol of the study was approved by the ethics com-mittee of Iran University of Medical Sciences. Written, in-formed consent was obtained from all participants.3.1. Statistical AnalysisNumerical variables were reported as mean ± stan-dard deviation (SD) when normally distributed, otherwiseas median plus range. The chi-square test was used to eval-uate the association between menarche age categories andfirst offspring sex. P ≤ 0.05 was considered to be statisti-cally significant. All analyses were performed using SPSSfor Windows version 14 (SPSS Inc., Chicago, IL, USA).4. ResultsAnalysis was performed on the complete data of 1,664of the 2,000 women included in our study. Mean age of thestudy population was 29.6± 7.09. Mean menarche age andparity were equal to 13.25± 1.21 and 1.59±0.8, respectively.Of all participants, 971 (57.9%) were 25 - 35 years of age,and 441 (26.5%) were 15 - 25 years of age. In this study, the ageat menarche in 18.4% (307) of the participants was under 13years, 77.2% (1,285) between 13 - 15, and 4.4% (72) over 15 yearsof age. Characteristics of the study population are shownin Table 1.The OSR was also calculated as the proportion of maleto female sex, which was 0.932 in this study population.The OSR was higher when the menarche age occurred ear-lier. This means that there is a first offspring sex trend to-ward the male sex when menarche occurs at an earlier age.Table 2 demonstrates the OSR in different menarche ageTable 1. Characteristics of Study Population (n = 1664)aCharacteristicsAge 29.6 (7.09)Gravidity 1.71 (1.00)Parity 1.59 (90.88)Menarche age 13.25 (1.21)Menarche age, No. (%)< 13 years 307 (18.4%)13 - 15 years 1,285 (77.2%)> 15 years 72 (4.4%)BMI 25.22 (5.03)Age of first pregnancy 23.09 (4.35)Age of first pregnancy, No. (%)< 20 years 378 (22.9)20 - 30 years 1,051 (63.2)> 30 years 232 (13.9)First OSR, male/female 0.932aValues are expressed as mean (SD) unless otherwise indicated.categories. This difference was statistically significant, asshown in theThe OSR is also influenced by first pregnancy age. Asshown in Table 2, in early pregnancy ages, OSR would behigher, which means first offspring sex has a statisticallysignificant trend toward male when pregnancy age is ear-lier.When the first pregnancy age for different menarcheages were compared, it showed an earlier pregnancy age inwomen with a menarche age under 13 years old. First preg-nancy age was 23.62± 4.49, 24.50± 4.48, and 24.30± 5.69in women with a menarche age < 13 years, 13 - 15 years, and> 15 years, respectively. This difference was statistically sig-nificant (P = 0.005).5. DiscussionThis study found that women with an earlier menarcheage will have an earlier first pregnancy age. The OSR washigher when the menarche age was younger, which meansthat there is a first offspring sex trend toward male whenthe menarche age is younger. At earlier pregnancy ages,OSR was higher, which means that there is a first offspringsex trend toward male when the pregnancy age is younger.The mean age of menarche is reported to vary amongdifferent nations. With Egyptian girls, it ranges from 12- 13.7 years of age (3), and in Iran, it was estimated to be2 Shiraz E-Med J. 2016; 17(1):e37365.Haghighi L et al.Table 2. First OSR in Different Menarche Ages and Different Pregnancy AgesFirst OSR (Male/Female) P ValueTotal 0.932Menarche age, y 0.0001< 13 1.1613 - 15 0.94> 15 0.35Age at first pregnancy, y 0.0001< 20 1.3120 - 30 0.54> 30 0.7around 13 years of age in a review done in 2002 (26). In thisstudy, the mean menarche age was 13.25± 1.21, which wasin line with previous results.The first male to female OSR was 0.932 in this studypopulation. This shows female dominancy in the studiedpopulation. A decline in male to female OSR has been re-ported in many countries, including Denmark, England,the USA, Germany, and Japan (14, 27-30). The etiology of themale sex reduction rate is not yet known, but it seems to bemultifactorial. Chronic exposure to toxic environmentalagents, including tobacco smoke (13), and generally highstress situations, such as that witnessed in connection withthe Kobe earthquake in Japan (31), or after the Bam earth-quake in Iran (32), could be responsible. Some studies havealso associated parental age to OSR. Matsuo et al. have in-vestigated 3,049 deliveries, and they found a male domi-nant OSR in Japanese society and have proposed that olderparental age is associated with reduced OSR (32). In thisstudy, the male to female OSR was 0.932, and this is consis-tent with the other studies that show male dominancy atyounger pregnancy ages.As this study’s results show, women at earlier menar-che ages have a higher probability of giving birth to aboy as their first offspring. Fukuda et al. studied 10,847premenopausal women in 2011, and they concluded thatwomen entering menarche outside the normal age range,especially those with earlier menarche, may have an in-creased chance of producing female offspring (13). In con-trast, this study shows earlier menarche age (under 13)causes the sex ratio of the offspring to trend towards male.However, in line with their study, this study shows that amenarche age over 15 trends toward the first offspring be-ing female. This difference may be caused by the differentstudy population ages. Their participants had a mean ageof 37.5± 7.2, compared with 29.6± 7.09 in this study.5.1. ConclusionAs OSR is an important social factor, larger studies indifferent ethnic populations are required to assess the ex-act associations between menarche age, first pregnancyage, and offspring sex ratio and also to evaluate other pos-sible underlying mechanisms.AcknowledgmentsThe authors wish to express their gratitude to all of thecolleagues who participated in this study and all the staffat the endometriosis research center at Akbarabadi HOSPI-TAL and Rasule Akram hospital in Tehran, Iran and Kasrahospital in Karaj, Iran.FootnotesAuthors’ Contribution: All authors have contributedequally to this study.Financial Disclosure: All authors declare that they haveno conflict of interest.Funding/Support: This article has been extracted from aresearch project approved and supported by the Iran Uni-versity of Medical SciencesReferences1. Sharma K, Talwar I, Sharma N. Age at menarche in relation to adultbody size and physique. Ann Hum Biol. 1988;15(6):431–4. [PubMed:3250324].2. 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The association between menarche age and first offspring sex ratio

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The association between menarche age and first offspring sex ratio

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