Serum Progesterone and Threatened Abortion During Lactation

Association Between Maternal Serum Progesterone Levels and Threatened Abortion in Lactating Pregnant Women

This study aims to evaluate the effect of first-trimester maternal serum progesterone levels on threatened abortion in women who conceive during the lactation period. Serum progesterone concentrations will be measured in lactating pregnant women during the first trimester, and their association with the etiology of threatened abortion will be analyzed.

Threatened abortion is defined as vaginal bleeding occurring in the first trimester of pregnancy and represents a risk for early pregnancy loss. Previous studies have shown that serum progesterone levels may be lower in cases of threatened abortion compared to healthy pregnancies and play an essential role in predicting miscarriage risk. Serum progesterone is therefore considered a useful biomarker for assessing pregnancy viability and prognosis.

During lactation, progesterone levels may vary depending on breastfeeding duration and maternal hormonal status, and generally remain low, similar to follicular-phase levels in non-pregnant women. However, normal reference values during lactation are not well established. This study aims to contribute new data to the limited literature on the relationship between lactation, serum progesterone levels, and threatened abortion, and to provide insights that may help improve early pregnancy loss prevention strategies.

Study Overview

• Status: Not yet recruiting
• Conditions: Threatened Abortion

Detailed Description

This study is designed to investigate the relationship between maternal serum progesterone levels and threatened abortion in women who conceive during the lactation period. The primary objective is to evaluate first-trimester serum progesterone concentrations in lactating pregnant women and to assess their role in the etiology and clinical course of threatened abortion.

Threatened abortion is characterized by vaginal bleeding during the first trimester of pregnancy and is associated with an increased risk of early pregnancy loss. Progesterone plays a critical role in the maintenance of early pregnancy by supporting endometrial receptivity, suppressing uterine contractility, and modulating maternal immune tolerance. Previous studies have demonstrated that serum progesterone levels tend to be lower in pregnancies complicated by threatened abortion compared to uncomplicated pregnancies, and that reduced progesterone concentrations may be predictive of subsequent miscarriage.

Lactation is associated with distinct hormonal changes, primarily mediated by elevated prolactin levels, which suppress ovulation and result in progesterone levels comparable to those observed during the follicular phase of the menstrual cycle. Although progesterone levels increase following conception, the hormonal milieu during lactation may influence progesterone production and regulation in early pregnancy. However, normal reference ranges for serum progesterone levels in lactating pregnant women have not been clearly established, and data regarding their association with threatened abortion remain limited.

In this study, pregnant women who conceive during the lactation period will be enrolled. Maternal serum progesterone levels will be measured during the first trimester, and participants will be evaluated for the presence or absence of threatened abortion, defined as first-trimester vaginal bleeding with a viable intrauterine pregnancy. Clinical, obstetric, and demographic data will be recorded to allow assessment of potential confounding factors.

By examining the relationship between serum progesterone levels and threatened abortion in lactating pregnancies, this study aims to provide new insights into the hormonal mechanisms underlying early pregnancy complications. The findings may contribute to improved risk stratification, early diagnosis, and management strategies for threatened abortion in this specific population. Additionally, the study seeks to expand the limited body of literature on lactation-associated hormonal changes during early pregnancy and their clinical implications.

• Study Type: Observational
• Enrollment (Estimated): 150

Contacts and Locations

• Study Contact: Name: Burak D Aydoğdu, M.D.; Phone Number: +90 539 618 2228; Email: burakd.1992@hotmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

The study population consists of lactating pregnant women aged 18 to 50 years who present for routine antenatal care during the first trimester of pregnancy at the participating obstetrics and gynecology clinics. Eligible participants include women who conceived while breastfeeding and have available first-trimester serum progesterone measurements. Participants will be prospectively followed to evaluate the occurrence of threatened abortion and early pregnancy outcomes.

Description

Inclusion Criteria:

• Female participants aged 18 to 50 years.
• Pregnant women who conceived during the lactation period.
• Singleton pregnancy.
• First-trimester pregnancy.
• Availability of first-trimester serum progesterone measurement obtained as part of routine antenatal care.
• Ongoing follow-up at the participating hospitals.

Exclusion Criteria:

• Age under 18 years or over 50 years.
• Multiple pregnancies.
• Known chronic medical diseases.
• Use of progesterone supplementation before serum progesterone measurement.
• Missing or incomplete clinical or laboratory data.

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Lactating Pregnant Women (First Trimester); Pregnant women who conceived during the lactation period and are in the first trimester of pregnancy. Maternal serum progesterone levels will be measured at enrollment. Participants will be prospectively followed to evaluate the occurrence of threatened abortion, defined as first-trimester vaginal bleeding with a viable intrauterine pregnancy. This is a prospective observational cohort study, and no interventions are assigned.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incidence of Threatened Abortion in Lactating Pregnant Women	The incidence of threatened abortion, defined as first-trimester vaginal bleeding with a viable intrauterine pregnancy, assessed by clinical evaluation and ultrasonographic confirmation.	From enrollment in the first trimester until 14 weeks of gestation

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
First-Trimester Serum Progesterone Levels	Maternal serum progesterone levels measured during the first trimester of pregnancy will be recorded and compared between women with and without threatened abortion.	At enrollment during the first trimester of pregnancy
Early Pregnancy Loss	The occurrence of pregnancy loss before 14 weeks of gestation will be recorded and evaluated in relation to first-trimester serum progesterone levels.	Up to 14 weeks of gestation
Serum Progesterone Cut-off Value for Predicting Threatened Abortion	The optimal first-trimester serum progesterone cut-off value for predicting threatened abortion in lactating pregnant women will be determined using receiver operating characteristic (ROC) curve analysis.	During the first trimester of pregnancy

Collaborators and Investigators

• Sponsor: Prof. Dr. Cemil Tascıoglu Education and Research Hospital Organization
• Investigators: Principal Investigator: Burak D. Aydoğdu, M.D., Prof. Dr. Cemil Tascıoglu Education and Research Hospital Organization

Publications and helpful links

General Publications

• Sammut L, Bezzina P, Gibbs V, Muscat-Baron Y, Agius-Camenzuli A, Calleja-Agius J. Predicting first-trimester pregnancy outcome in threatened miscarriage: A comparison of a multivariate logistic regression and machine learning models. Radiography (Lond). 2025 Oct;31(6):103159. doi: 10.1016/j.radi.2025.103159. Epub 2025 Sep 4.
• Jiang TT, Zhang DY, Liu ZY, Lu ZS, Yan LM, Sun S, Xie JA, Zhu M, Zhang ZH, Wan YH, Wang H, Hao JH, Zhang C. Association of co-exposure to EDCs in early pregnancy with threatened abortion: The mediation effect of progesterone. Environ Int. 2025 Dec 11;207:110001. doi: 10.1016/j.envint.2025.110001. Online ahead of print.

Study record dates

Study Major Dates

• Study Start (Estimated): January 1, 2026
• Primary Completion (Estimated): December 31, 2027
• Study Completion (Estimated): January 1, 2028

Study Registration Dates

• First Submitted: January 14, 2026
• First Submitted That Met QC Criteria: January 14, 2026
• First Posted (Actual): January 22, 2026

Study Record Updates

• Last Update Posted (Actual): January 26, 2026
• Last Update Submitted That Met QC Criteria: January 23, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: Threatened Abortion; Serum Progesterone Levels; Lactation During Pregnancy
• Additional Relevant MeSH Terms: Urogenital Diseases; Female Urogenital Diseases and Pregnancy Complications; Pregnancy Complications; Abortion, Threatened
• Other Study ID Numbers: 2025/517

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Although data would be de-identified before any potential sharing, individual participant data will not be shared because the original ethics committee approval and informed consent do not permit data sharing beyond the study team. In addition, the dataset contains detailed clinical and laboratory variables that could carry a risk of re-identification. Any future data sharing would require additional ethics committee approval and updated participant consent. Study results will be disseminated in aggregated and anonymized form through scientific publications.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No