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Table 1 Characteristics of studies included in the meta-analysis

From: Association between abnormal body mass index and pregnancy outcomes in patients following frozen embryo transfer: a systematic review and meta-analysis

Study Country Year Definition of normal BMI Low BMI Normal weight High BMI Patients Embryo stage Autologous or donor oocytes cycle Ovarian status of the patients Cycle rank Endometrial preparation
Chen et al. [22] China 2018 18.5–24 NA 21.1 ± 1.5 26.8 ± 2.3 Inclusion: Age ≤ 35 years, with PCOS, First IVF/ICSI cycles, GnRH-ant protocol for COH
Exclusion: Congenital adrenal hyperplasia, androgen secreting tumors, or Cushing’s syndrome
Both Autologous Only PCOS All depends on patients' condition
Insogna et al. [23] USA 2017 18.5–24.9 Not specified Not specified Not specified Inclusion: All consecutive FBT cycles
Exclusion: Incomplete information cycles, cancelled cycles
Blastocyst Both Both All HRT after pituitary suppression
Jin et al. [24] China 2019 18.5–23.9 Not specified Not specified Not specified Inclusion: Age < 35 years; tubal factors or primary infertility; poor semen quality; retro grade ejaculation or obstructive azoospermia for ICSI; normal menstrual cycle
Exclusion: PCOS; endometriosis; endocrine abnormalities; chromosome polymorphism or chromosome abnormalities; adverse pregnant production history; ovarian dysfunction; ovarian surgery or uterine malformation; donated oocytes
Both Autologous Not PCOS First depends on patients' condition
Lin et al. [25] China 2019 18.5–24.9 NA 21.45 ± 1.7 28.6 ± 2.1 Inclusion: PCOS; Age 20–35 years; first FET cycles
Exclusion: History of unilateral oophorectomy; abnormalities of the uterus; karyotypic abnormalities; recurrent pregnancy loss; any conditions which precluded the safety of pregnancies or ART
Both Autologous Only PCOS First HRT or mild stimulation
Oliva et al. [33] USA 2020 18.5–24.9 Not specified Not specified NA Inclusion: Age 20–46 years, all patients with a documented BMI
Exclusion: BMI ≥ 25 kg/m2
Blastocyst Autologous Not specified Not specified HRT
Ozgur et al. [26] Turkey 2019 18.5–24.9 Not specified Not specified Not specified Inclusion: Age 18–42 years, First FET, ICSI cycles
Exclusion: Not specified, only single blastocyst transfers were analyzed in live birth rate
Blastocyst Autologous Not specified First HRT after pituitary suppression
Prost et al. [27] France 2020 18.5–24.9 NA 21.5 ± 1.8 34 ± 3.1 Inclusion: All consecutive autologous FBT cycles
Exclusion: Oocyte donation, natural or stimulated, PGT cycles; risk factors for recurrent pregnancy loss
Blastocyst Autologous Both All HRT
Qiu et al. [28] China 2019 18.5–24.9 17.62 ± 0.8 21.86 ± 1.8 28.1 ± 1.6 Inclusion: PCOS
Exclusion: Serious and unstable disease; gynecological borderline and malignant tumors; other metabolic disorders; chromosomal abnormalities; congenital uterine malformations
Both Autologous Only PCOS First HRT or mild stimulation
Tang et al. [29] China 2021 18.5–24.9 17.53 ± 3.1 21.61 ± 1.7 26.37 ± 1.9 Inclusion: Age 20–40 years, FSH < 10 IU/L
Exclusion: Lack of antral follicles or FSH > 10 IU/L; diabetes or hypertension; recurrent pregnancy loss; endocrine abnormalities; drugs or diseases that can cause underweight
Both Autologous Not PCOS First depends on patients
Rittenberg et al. [30] UK 2011 18.5–24.9 NA 21.6 ± 1.9 27.8 ± 2.2 Inclusion: Single blastocyst transfer
Exclusion: Age > 40 years, BMI < 18.5 kg/m2; PGD, donated oocytes; embryos frozen for fertility preservation; monozygotic twin gestation
Blastocyst Autologous Both Not specified HRT after pituitary suppression
Wang et al. [31] China 2017 18.5–24.9 NA 21.28 ± 0.0 27.13 ± 0.1 Inclusion: Age < 40 years; FSH < 10 IU/L; AFC of more than 3; regular menstrual cycles; male, unexplained, or tubal factors infertility
Exclusion: Accept HRT treatments in previous 3 month; PCOS; functional ovarian cyst with E2 > 100 pg/mL; PGD, IVM, donor cycles; any contraindications to ovarian stimulation treatment; presence of fresh embryo transplantation
Both Autologous Not PCOS Not specified depends on patients' condition
Zhang et al. [32] China 2019 18.5–22.9 17.66 ± 0.7 20.67 ± 1.2 25.68 ± 1.5 Inclusion: First FET cycles, high quality embryo
Exclusion: Age > 40 years; recurrent pregnancy loss; previous IVF attempts; submucosal fibroids or polyps, intramural fibroids > 4 cm, hydrosalpinx, and congenital uterine malformation; hypertension; diabetes; thyroid dysfunction
Both Autologous Both First depends on patients' condition
  1. Note: BMI body mass index, E2 estradiol, PCOS polycystic ovary syndrome, COH controlled ovarian hyperstimulation, ART assisted reproductive technology, FET frozen embryo transfer, FBT frozen blastocyst transfer, GnRH gonadotropin-releasing hormone, FSH follicle-stimulating hormone, ICSI intracytoplasmic sperm injection, IVF in vitro fertilization, AFC antral follicle count, NA not applicable, PGD Preimplantation Genetic Diagnosis, PGT Preimplantation Genetic Testing, IVM in vitro maturation, HRT Hormone replacement therap