The present study was a prospective observational study involving 154 singleton pregnant women who attended Peking University First Hospital from January 2016 to December 2019. The study was conducted in accordance with the Declaration of Helsinki. Our study was approved by the Peking University First Hospital Human Research Ethics Committee, informed consent was obtained from all of the participants. The inclusion and exclusion criteria are shown in Fig. 1. We included fetuses between 21 weeks and 28 weeks of gestational age for two reasons. First, pregnant women underwent a second trimester ultrasound scan between 21 weeks and 23 weeks in our hospital; therefore, a fetus could be first diagnosed with mild ventriculomegaly at 21 weeks. Second, based on a previous study8 and our experience, some sulci and gyri, such as the calcarine sulcus, could develop to grade 4 or 5 (maximum development) after 28 weeks, as it is of little value to assess the cortical development process of IMVM fetuses who are diagnosed after 28 weeks. In total, we included 40 singleton pregnant women. The clinical information of each participant, including name, age, reproductive history and family history of nervous system disease, was recorded after inclusion. The gestational (postmenstrual) age was determined as the time from the first day of the last menstruation and was confirmed by a crown–rump length (CRL) measurement in the first trimester.
Ultrasound examinations were carried out at an interval of 2–3 weeks using GE Voluson E8 and E10 (GE Healthcare) through transabdominal and transvaginal ultrasonography after the initial detection of ventriculomegaly. Regular ultrasound including biometry measurements was carried out, followed by neurosonography. Transabdominal neurosonography was performed with 3–5-MHz probes. Transvaginal neurosonography was performed with 5–9-MHz probes.
As a general neurosonographic assessment, the distal lateral ventricle atrial width was obtained in the transventricular plane, and the proximal lateral ventricle was assessed using coronal planes11–13. Progression of ventriculomegaly was defined as ventricular enlargement of greater than 2 mm compared with the initial measurement. Stable ventriculomegaly was defined as an enlargement of less than 2 mm, and regressive ventriculomegaly was defined as a decrease of 2 mm or more or as a ventricular diameter of less than 10 mm9, 14.
We also assessed the maturation of the parieto-occipital, calcarine and cingulate sulcus of both hemispheres of the IMVM fetuses at the specific planes according to the scoring method described by L. R. Pistorius8. The sulci that we chose to examine were close to the midline, which would not be shaded by the fetal skull and enables their continuous assessment throughout the entire pregnancy through transabdominal and transvaginal neurosonography. The parieto-occipital sulcus was evaluated on the axial cephalic plane, the calcarine sulcus was evaluated on the coronal transcerebellar plane, and the cingulate sulcus was evaluated on the coronal transcaudate and transthalamic plane. A subjective score ranging from grade 0 to grade 5 was used to assess the cortical development, where 0 is no development and 5 is the highest grade of maturation. More specifically, the sulcus of grade 0 is not visible, the sulcus of grade 1 displays a shallow indentation or echogenic dot shape, the sulcus of grade 2 exhibits a Broad V (width ≥ depth) shape, the sulcus of grade 3 has a Y or narrow V (depth > width) shape, the sulcus of grade 4 has an I- or J-shape, and the sulcus of grade 5 shows branches on the basis of grade 4. Asymmetric sulcal maturation of two hemispheres was defined as a difference of at least one grade between any sulci of two hemispheres. Furthermore, the fetuses were divided into the symmetric maturation group and the asymmetric maturation group.
Magnetic resonance imaging (MRI)
Fetal MRI was performed using a 1.5-T MRI System (Philips Multiva) with a 32-channel cardiac-phased array surface placed over the gravid uterus for signal reception. The fetal head at the scanning center was scanned in the coronal, transverse, and sagittal planes by Half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences (repeat time of 1500 ms, echo time of 107–160 ms, slice thickness of 3 mm, slice gap of 0 mm, matrix of 280 × 205). Additionally, the fetal head was scanned in the transverse plane by T1 fast field echo (T1-FFE) sequences (repeat time of 15 ms, echo time of 7.5 ms, slice thickness of 3 mm, slice gap of 0 mm, matrix of 160 × 151) and diffusion weighted imaging (DWI) sequences (repeat time of 3249 ms, echo time of 90 ms, slice thickness of 3 mm, slice gap of 0 mm, matrix of 92 × 72). A 24 cm to 30 cm field of view (FOV) was used.
Genetic and TORCH examination
Genetic examinations were performed in all cases to exclude common genetic abnormalities, including karyotype analysis, comparative genome hybridization array analysis and single nucleotide polymorphism array analysis, referring to the Database of Genomic Variants, Decipher Database, Online Mendelian Inheritance in Man (OMIM) database, PubMed, and other databases. Additionally, TORCH (toxoplasmosis, other, rubella, cytomegalovirus and herpes simplex virus) examination was performed in all cases to exclude common infection.
Data on pregnancy outcomes (gender, Apgar score and perinatal and neonatal morbidity and mortality) were recorded for all cases. Pediatricians from the Department of Pediatrics in our hospital, with professional training, evaluated the neonatal behavioral neurological assessment (NBNA) scores for each included infant, including the general condition, action behavior, muscular tension, and primitive reflex, within seven days of age. Each parameter was assigned 0–2 points, with a total score of 40 and a score of greater than 36 being normal. The peripheral environment was kept quiet, and the temperature was maintained at a suitable level. The room temperature was maintained at approximately 26 °C. All evaluation parameters were assessed in sleeping children at 1 h after being fed.
Cranial ultrasound examinations of infants were performed by an experienced sonographer on an ATL 5000 Unit (Philips, Best, The Netherlands) within 6 months of age. Abnormalities of the neonatal brain were recorded.
At 6, 12 and 18 months after birth, all the included infants were assessed using the Ages and Stages Questionnaire, Third Edition (ASQ-3). Parents answered 30 questions covering 5 domains of development, including communication, gross motor, fine motor, problem-solving, and adaptive skills. Parents were instructed to try activities with their child to facilitate an accurate assessment. A pass/fail score was assigned for each area of development. The presence of a problem in any domain screened, 2 SDs below the mean area score, was considered to indicate delayed development. Moreover, some of the included children were assessed with Bayley Scales of Infant Development (BSID-I) at 6, 12 and 18 months old. Experienced physicians in our hospital used the BSID-I to assess neurodevelopment, including the mental developmental index (MDI) and psychomotor developmental index (PDI). Scores of less than 79 on the MDI or PDI were considered to indicate a low level of development. Others were unable to undergo this assessment due to the COVID-19 outbreak or because they lived far from our hospital.
Data analyses were performed using SPSS version 21 for Mac (SPSS Inc., Chicago, IL). Categorical variables are expressed as percentages and continuous variables as means or median values. Student’s t-test for independent samples and Pearson chi-square tests were used to compare quantitative and qualitative data between the symmetric maturation and asymmetric maturation groups.