Prospective Twin Pregnancy Cohort at Montpellier University Hospital

Maternal extern exposome

Exposure to air pollutants (NO₂, PM₂.₅, O₃, VOCs) during the two years prior to and during pregnancy: these values will be derived from the Chimera model, and an area under the exposure curve will be calculated. The level of exposure will be calculated based on the mother's home addresses during the two years prior to inclusion, at the time of inclusion, and based on her work addresses during pregnancy if she worked for more than four months during pregnancy. These data will be assessed individually and incorporated into a statistical model. Data from the patient follow-up log, data from questionnaires: * Environment, general health, lifestyle, and diet. * Obstetric, medical, and surgical history, current pregnancy. These data will be assessed individually and incorporated into a statistical model.

Maternal intern exposome

Amount of lead in urine at 25 weeks of gestation. Lead will be measured by Montpellier University Hospital in a urine sample taken during the sixth month of pregnancy (inclusion) using ICP-Ms. These data will be assessed individually and incorporated into a statistical model.

Abnormal newborn weight

Growth retardation: Abnormal birth weight (in kg) for at least one of the two children (\< 3rd percentile according to the Olsen curve).

Abnormalities in children

* Occurrence of one or more altered anthropometric characteristics (outside reference values) at birth: fetal macrosomia, abnormal height, abnormal head circumference. * Occurrence of one or more altered anthropometric characteristics (outside reference values) at D+15, 1, 3, 6, 8, 10 months and 1 year: abnormal weight (\<3rd or \>97th percentile, Olsen curve), abnormal height (\<5th or \>95th percentile), abnormal head circumference (\<5th or \>95th percentile). * Occurrence of a serious health problem at birth or during the first year of life. * Knowledge of occurrence of one or more of the following conditions during the first year: ENT, respiratory, gastroenterological, dermatological conditions, recognized atopy/allergies, early neurodevelopmental disorder. All these data will be assessed individually and incorporated into a statistical model.

Obstetric complications

Occurrence of at least one of the obstetric complications listed in the patient follow-up record.

Comparison of the Twins

* Type of pregnancy from which the twins originate: monochorionic (monoamniotic or biamniotic) or dichorionic. * Sex of twins: 2 girls, or 2 boys, or 1 girl and 1 boy

Children's extern exposome

Exposure to air pollutants (NO2, PM2.5, O3, VOCs) throughout pregnancy and during the first year of life: these values will be derived from the Chimera model, and an area under the exposure curve will be calculated. The level of exposure will be determined based on the mother's personal and professional addresses during pregnancy and the first year of the children's lives. These data will be assessed individually and incorporated into a statistical model. Data from the patient follow-up log, data from questionnaires: • Environment, lifestyle, diet, treatments received, games and care. These data will be assessed individually and incorporated into a statistical model.

Supplement to the mother's exposome

Epigenetics: Maternal epigenome, characterization of the genome in a blood sample taken at delivery. Epigenetic analyses will be outsourced to a competent laboratory. Methylation sequencing will be performed using the Xgen Methyl-Seq DNA kit (IDT DNA). These data will be assessed individually and incorporated into a statistical model. Nutrient and Contaminant Profiling: * Nutrients (carbohydrates, amino acids, vitamins, minerals, fatty acids) in maternal blood at delivery. Analyses outsourced to a competent lab using methods specific to each nutrient type. * Heavy metal exposure: * Chronic: lead in urine; acute: heavy metals in blood (see "8. Children's internal exposome"). * Maternal-fetal transfer: heavy metals in placenta, analyzed by a competent lab, using a specific method. These data will be assessed individually and incorporated into a statistical model.

Supplement to the children's exposome

* Epigenome : obtained from umbilical cord blood at birth ; analyses outsourced to a competent lab. Methylation sequencing with Xgen Methyl-Seq DNA kit (IDT DNA). Data assessed individually and integrated into a statistical model. * Maternal metabolites : assessed in urine collected at inclusion ; outsourced to a competent lab. Urinary metabolomics (untargeted or targeted small metabolites) via LC-MS/MS, GC-MS, or ¹H-NMR on spot or 24h urine, creatinine-normalized, to profile maternal metabolism and exposome. Data assessed individually and modeled statistically. * Twins' microbiome : meconium at birth and stool at 6 months and 1 year ; analyzed by specialized external lab via sequencing. Data assessed individually and modeled statistically. * IgA and IgE: quantified in milk during newborns' stay; analyses by Montpellier University Hospital. Data assessed individually and modeled statistically.

PM and PMT substances

Chemical contaminants in the environment (Persistent and Mobile (PM) and Persistent Mobile and Toxic (PMT)) will be quantified from a 5 ml urine sample taken from pregnant women. The urine sample will be analyzed by Elena Gomez's team at UMR 5151 Hydrosciences in Montpellier.