Study population
Infertile women seeking IVF treatment in Peking University Shenzhen Hospital in Guangdong, China, from September 2016 to December 2017, were invited to participate in an ongoing prospective cohort study investigating the relationship between maternal Mediterranean dietary pattern and IVF outcome. The inclusion criteria were as follows: (1) age ≤ 40 years; (2) body mass index (BMI) ≤30 kg/m2; (3) use antagonist protocol or long protocol for ovarian stimulation; (4) keep dietary habit unchanged in at least recent 12 months. The study protocol was approved by the Ethics Committee of Peking University Shenzhen Hospital. Written informed consent were obtained from the participants and questionnaires were processed anonymously.
Questionnaires and assessment of adherence to MediDiet
A food frequency questionnaire (FFQ) was designed by cooperating with specialists from the department of Nutrition in the hospital, according to the characteristics of Mediterranean dietary pattern and food composition table of China, edition 2015. The FFQ included questions about common consumed food groups (69 items regarding consumption of cereals, meat, fish, legumes, fat, fruits, nuts, vegetables, dairy products, eggs and alcoholic beverages). The frequency of food intake was expressed as times per day, times per week or times per month and the consumed amount each time were recorded as grams or milliliters.
When the patient decided to undergo IVF treatment, the FFQ was provided to and filled out by every participant to estimate the dietary pattern. The adherence to Mediterranean diet was evaluated as previously described [10] with little modification. Briefly, a score of 0 or 1 was assigned to each item of 9 components. A value of 1 was assigned when consumption was at or above the median in 5 components (cereal, legumes, vegetables, fruits and nuts, and fish) or below the median in 2 components (red meat and dairy products), and 0 was scored on the opposite situation. For fat intake, 1 score was assigned when the ratio of unsaturated lipids to saturated lipids was above the median and 0 score was assigned otherwise. There was a component about alcoholic beverage in the previous score system. Since the benefit of moderate alcohol intake to female fertility was challenged by more and more evidence [21], this item was excluded in this study. Finally, a total score range from 0 to 8 was obtained. Women with this score above the median were allocated to higher MediDiet adherence group, and those who with the score below the median were in lower MediDiet adherence group.
IVF procedure and data extracted
IVF treatment was administrated to infertile women according to the standard operating procedure of Reproductive Center in the hospital. Ovarian reserve was tested and then protocol for controlled ovarian hyperstimulation (COH) was decided. Only those received GnRH agonist long protocol would be included. Patients were treated with 1.25 mg of Diphereline (IPSEN PHARMABIOTECH, France) on about day 21 of menstrual cycle. After the serum E2 was lower than 50 pg/ml, 75–225 IU of recombinant human follitropin (GONAL-f, Merck Serono, Switzerland) was administered according to individual response. Oocyte maturation was induced by injection of 5000–10,000 IU of HCG (Livzon Pharm, China) when the two leading follicles were 17 mm in mean diameter. Oocytes were aspirated 36 h later under the guidance of a B-ultrasound. Insemination method (IVF or ICSI) was decided according to the quality of sperm. Embryo quality was assessed on 3 days after oocyte retrieval. An embryo composed of 7–9 blastomeres and scoring with grade I or grade IIa was defined as top quality embryo. Data about female age, type of infertility, body mass index (BMI), duration of infertility, antral follicle count (AFC), basal and HCG day gonadal hormone levels, gonadotropin (Gn) duration and dosage, male age, sperm parameters, number of oocytes retrieved, insemination method, embryonic development and clinical outcomes including clinical pregnancy and implantation rate were collected for subsequent statistical analysis.
Statistical analysis
Statistical Package for Social Science (SPSS) software, version 25.0 (IBM, Armonk, New York, USA) was used to perform all the statistical analysis. The results of continuous variables were presented as mean value ± standard deviation (SD). Categorical data were expressed as absolute frequencies and proportional rates. If continuous data complied with normal distribution, Student’s t-test was used. If not, Mann-Withney U test was applied. Categorical data were compared by a Chi-squared test. Pearson correlation test was used to estimate the correlation between adherence to MediDiet and those parameters with P < 0.10 in univariate analysis. A multivariate linear regression analysis was used to further estimate the influence factors on embryo yield. All reported P values were two tailed, and P < 0.05 was established as the level of significance.