Swine Flu (H1N1) Infection During Pregnancy

SGSwine Flu (H1N1) Infection During Pregnancy:

Background: Pregnancy can significantly impact the immunity of a woman leaving her susceptible to seasonal flu as well as swine flu. Swine Influenza (Swine flu) is a respiratory disease in pigs caused by Type A influenza virus (1). This virus causes regular outbreaks in pigs but occasionally, pigs transmit influenza virus to humans. The swine flu virus first emerged among people in Mexico during the spring of 2009 and spread with travellers worldwide, resulting in the first influenza pandemic since 1968. Scientists recognized a particular strain of flu virus known as H1N1 which was found to be a combination of viruses from pigs, birds and humans. During the 2009-10 flu season, H1N1 caused the respiratory infection in humans that was named as swine flu. According to US Centres for Disease Control and Prevention, World Health Organisation has determined that swine influenza A virus is contagious and easily spreads from person to person (2).


Patients with novel H1N1 typically present with symptoms of an acute respiratory illness, such as cough, sore throat, fever and headache, fatigue, body aches, vomiting, and diarrhea. Symptoms commonly develop within one week of exposure, and patients are contagious for approximately 8 days thereafter (2). The pandemic (H1N1) influenza virus differs in its pathogenicity from seasonal influenza in (a) targeting a wider age ranging from children to young adults and (b) infecting the lower respiratory tract causing rapidly progressive pneumonia especially in children, young adults and pregnant women (1). The chances of virus contamination is higher if lived in or travelled to an area where many people are affected by swine flu or coming in close proximity with pigs/pig farms.

Effects on Pregnancy: In pregnant woman, immunity is suppressed due to the developing fetus. As a result of the hormonal and physical changes, they are at greater potential risk of developing complications. The enlarging uterus presses on the diaphragm and together with changes in the lungs which make the woman more prone to complications such as pneumonia and Adult Respiratory Distress Syndrome (ARDS). Pregnancy-related complications of novel H1N1 infection include non-reassuring fetal testing (most commonly fetal tachycardia) and febrile morbidity. Hyperthermia in early pregnancy has been associated with neural tube defects and other congenital anomalies, and fever during labor and birth is a risk factor for neonatal seizures, newborn encephalopathy, cerebral palsy, and death. In a series of 5 pregnant women recently hospitalized for pandemic H1N1, the CDC reported that 2 women developed complications including spontaneous abortion (at 13 weeks) and premature rupture of membranes (at 35 weeks). (3,4)


If influenza is suspected in a pregnant patient, she should undergo immediate testing for novel H1N1. A rapid influenza antigen test is commonly used in patients suspected of having influenza, which should be confirmed by reverse transcription polymerase chain reaction (RT-PCR). (3)


Chemoprophylaxis: All pregnant women should be screened and treated because the potential benefit outweighs the theoretical risk to the fetus. Four antiviral agents are usually recommended, zanamivir, oseltamivir, peramivir and baloxavir marboxil. Two regimens are recommended by CDC for infected pregnant women: zanamivir (5-mg inhalations twice daily for 5 days) or oseltamivir (75 mg twice daily for 5 days) (4). Although, zanamivir may be the drug of choice due to its limited systemic absorption but inhaled route of administration is not recommended, especially in women suffering from asthma or chronic obstructive pulmonary disease. Novel H1N1 influenza A is resistant to adamantanes, such as amantadine and rimantadine. Chemoprophylaxis should probably be continued for 10 days after the last known exposure. In addition to specific antiviral medications, acetaminophen can be administered if the patient is febrile. Close monitoring for symptoms of swine flu is recommended. Please note that do not take any medication without consulting physician. Breastfeeding is considered safe during medication as there are no reports on effect of antiviral drugs on breast milk.


Guidelines for prevention of H1N1 infection in pregnant women are similar to those for seasonal flu. It is advised to use facemask, cover their cough, practice good hand hygiene, restrict travelling in public places and minimize sick contacts (6). H1N1 vaccination is also highly recommended as such vaccinations are low-cost interventions and are shown to have substantial benefits for both mother and baby (7). Compared to a healthy adult a pregnant woman is at higher risk of infection with the novel H1N1 influenza A virus. Thus, it is very crucial to be prepared with adequate information in order to provide the care necessary to address the increased morbidity, mortality and pregnancy related complications faced by pregnant women during such an influenza pandemic.

Dr. Somenath Ghatak, Ph.D (Life Sciences), All India Institute of Medical Sciences, New Delhi, India.

March 13, 2019


  • 1. Pregnancy, childbirth, postpartum and newborn care. A guide for essential practice. WHO, UNPF, UNICEF, and the World Bank. Geneva, Switzerland, 2009.:
  • 2. Infection prevention and control in health care for confirmed or suspected cases of pandemic (H1N1) 2009 and influenza-like illnesses. World Health Organization, 16 December 2009. Available at:
  • 3. Clinical management of human infection with pandemic (H1N1) 2009: revised guidance. World Health Organization, November 2009. Available at:
  • 4. Further infection prevention and control guidance is available from WHO website at
  • 5. Carlson A, Thung SF, Norwitz ER. H1N1 influenza in pregnancy: what all obstetric care providers should know. Rev Obstet Gynecol. 2009; 2(3): 139-145. PMCID: 19826571
  • 6. Centers for Disease Control and Prevention Web site, authors. Pregnant women and novel influenza A (H1N1): considerations for clinicians.
  • 7. Mak TK, Mangtani P, Leese J, et al. Influenza vaccination in pregnancy: current evidence and selected national policies. Lancet Infect Dis. 2008;8:44–52.