In vitro fertilization pregnancy may cause fetal thymic volume involution: A case-control study

Abstract Background The effect of modern infertility treatment modalities on fetal thymic volume has not been well known. Objective 3-dimensional (3D) fetal thymus volumes of 18-24 wk in vitro fertilization (IVF) pregnancies and spontaneous pregnancy cases were compared. Materials and Methods 135 cases were evaluated in this prospective case-control study. The study was conducted between July 2019 and July 2020 at a university hospital in Trabzon, Turkey. Fetal thymus volume was calculated in the pregnant cases included in the study with the help of the virtual organ computer-assisted analysis system included in the advanced ultrasonography system. The fetal thymus volumes were compared between pregnant women with IVF and spontaneous pregnant women. Results The fetal thymus size was significantly lower in the IVF pregnancy group than in spontaneous pregnancy cases (p < 0.001). It was found that the fetal complications, such as non-reassuring fetal health status and requirement for neonatal intensive care, were higher in cases who became pregnant after IVF treatment. It was also found that the rate of any pregnancy complication was significantly higher in IVF pregnancy group (p = 0.02). Conclusion In light of these results, it may be concluded that small fetal thymus size may be another fetal complication of IVF pregnancies.


Introduction
Assisted reproductive techniques (ART) define the clinical and laboratory methodologies employed in infertile couples to eliminate and rectify causes that prevent them from achieving pregnancy.Each year, more than 200,000 babies are born with ART globally, and today, this number is approximately 5 million (1,2).
An increased complication rate has been observed (such as preeclampsia, intrauterine growth restriction (IUGR), abnormal placental location, preterm birth, and low birth weight) in those who become pregnant with ART (3).
Studies comparing babies born from pregnancies obtained with in vitro fertilization (IVF) with the general population show that the rate of congenital anomalies is higher in this group than in the general population (4,5).
The microinjection technique applied to the oocyte in intracytoplasmic sperm injection cycles and the morphological disorders of the sperm/oocyte affect the development quality of the embryo.Physical damage to the cytoplasm may be possible following a traumatic injection.As a result of these potential risks, it is predicted that zygotes obtained following the intracytoplasmic sperm injection procedure are exposed to nonlethal cell damage and impaired embryonic development (6).Previous studies have shown an increased risk of complications, such as preeclampsia, IUGR, abnormal placental location, and low birth weight in those who become pregnant by using ART (3,(7)(8)(9)(10).
In pregnancy, the development process of the fetus's defense system during the intrauterine period focuses on adapting to the existing environment.The fetal thymus assumes the most important role in this immune system.One study showed that the thymus is smaller in various fetal and neonatal diseases (11).In literature, limited studies are found on fetal thymus volume in IVF pregnancies.This study had significant methodological problems, was a retrospective study, and its results were based partly on simple and subjective fetal thymus measurement (11,12).However, considering that the thymus is a 3-dimensional (3D) structure, 2D evaluation may not provide sufficient information.There is no literature study evaluating the use of 3D virtual organ computer-assisted analysis system (VOCAL) measurement for fetal thymus in IVF pregnancies.
The study aimed to compare the sonographic 3D fetal thymus size in second-trimester spontaneous and IVF pregnancies.

Materials and Methods
Totally 135 cases (18-24 wk pregnant women without any high-risk pregnancy risk factors) were evaluated in this prospective case-control study.

Ethical considerations
The study procedure was approved by the Ethical Committee of Karadeniz Technical University, Trabzon, Turkey (Approval no: 2019/205).A written informed consent was obtained from all the participants.

Statistical analysis
All the data were encoded and entered into SPSS software (version 13.0, Inc., Chicago, Illinois, USA).The statistical analyses were made on the computer using the Chi-square and Student t test.
International Journal of Reproductive BioMedicine Kaya et al.
other.A p-value of less than 0.05 was considered statistically significant.The data were presented as percentages, ratios, and mean ± SD.

Results
A

Discussion
This study showed that fetal thymus size change, which wss an important part of the fetal defense system, was affected by IVF pregnancies.
In  (20,21).In cases of acute stress due to infection and noninfection, there was a histological reduction in the thymus volume.The thymus is very important for the maturing immune system (22).
Although the effects of impaired thymus development on life-long immunological competence in fetuses that have growth restriction were not elucidated completely, one prospective study shows that immune function in later life is programmed in the early period (23).The result of a study suggested that the thymus is a mediator in the relation between atopic, autoimmune, and infectious diseases in infancy and childhood and fetal malnutrition (24,25).
Although thymus size was previously investigated in naturally conceived patients having maternal diabetes or rheumatic disease, there are no studies in the literature other than that of Nau and co-workers conducted in 2018 with patients who achieved pregnancy with IVF (12,(26)(27)(28)(29)(30).
The study of Nau et al., found that the fetal thymus size was smaller in cases who became pregnant by the IVF method at significant levels when compared to spontaneous pregnancies.
Although this study's results support the present study's results, the thymus size was evaluated retrospectively in the abovementioned study, and thymic thoracic ratio was calculated using 2D sonographic measurements (12).One of the limitations of our study was the small sampling.The number of patients could not be collected at the planned level because of the decreased number of patients who applied to the clinic due to the coronavirus pandemic, which swept the entire world, and the decreased number of patients who underwent IVF treatment.

Conclusion
The present study showed a relationship between IVF pregnancies and fetal sonographic 3D thymus volume.It was found that the fetal thymus size is significantly lower in cases who become pregnant after IVF treatment compared to spontaneous pregnancies.
It may be concluded that according to the results of this study, fetal thymus 3D volume measurement may be useful in detecting healthy pregnancies and predicting possible neonatal complications.In IVF pregnancies because pregnancy complications are increased, and fetal thymus volume is lower in IVF pregnancy cases at significant levels when compared to spontaneous pregnancies.
The study was conducted between July 2019 and July 2020 at a university hospital in Trabzon, Turkey.Participants in the study group were divided into 2 groups (n = 37/each): a) conceived with IVF and b) conceived spontaneously.Since it is forbidden in our country to use donated egg or embryo, their own embryo was used in IVF cycles.A total of 74 healthy pregnant cases were included according to the inclusion and exclusion criteria of the study.The main criteria for inclusion in the study were being of reproductive age (between 18-35 yr of age) and not having any International Journal of Reproductive BioMedicine Fetal thymus volume and IVF high-risk pregnancy factors and applying for routine pregnancy follow-up.Exclusion criteria for the study were the presence of any systemic disease (diabetes, hypertension, etc.), additional organ disease (heart, adrenal, thyroid, lung, kidney, blood, etc.) or history of drug use other than routine drugs used during pregnancy, or a history of alcohol use, smoking, or abnormal findings in routine biochemical/hematological test results, or abnormal pregnancy findings (multiple pregnancy, presence of anomaly in the fetus, abnormalities in pregnancy screening tests), or unwillingness to participate in research processes.In this way, 135 cases were evaluated and 61 of them were not included in the study because they did not meet the above criteria.Demographic data of all cases (age, height, weight, systolic/diastolic blood pressures, number of previous pregnancies, etc.) and routine fetal ultrasonographic measurement, gestational age determination data, and fetal 3D fetal thymus volume measurement data were recorded.The pregnancy and birth of all pregnant women were performed in our clinic, and pregnancy follow-up, pregnancy complications, and birth information were recorded.Apgar scores at the 1 st and 5 th min during delivery, newborn weights, cord blood pH, and base excess values were recorded.

Fetal
thymus volume was measured with the technique described in detail in our previous study (Figure 1) (13).Non-reliable fetal status formerly non-reassuring fetal status or fetal distress was defined as persistent or worsening category II or III fetal heart rate pattern.

Table I .
The comparison of IVF and spontaneous pregnancies regarding demographic and sonographic factors *Mean ± SD data were given.Student t test was used for comparison.**Data presented as n (%).Chi-square test was used for comparison.The interquartite ranges were a 2 and b 1.7.IVF: In vitro fertilization, EFW: Estimated fetal weight, BPD: Biparietal diameter, FL: Femur length, HC: Head circumference, AC: Abdominal circumference, BE: Base excess, APGAR: Appearance, pulse, grimace, activity, and respiration, C/S rate: Cesarean section rate International Journal of Reproductive BioMedicine Fetal thymus volume and IVF

Table II .
The comparison of IVF and spontaneous pregnancies in the study group regarding pregnancy complications