Vaccinations during pregnancy can help protect babies once they are born and more susceptible to these illnesses.
Yet more than 70 per cent of women carrying twins are not vaccinated against whooping cough or the flu, despite being fully funded under the national immunisation program.
A University of Queensland study examined almost 11,500 babies born from twin pregnancies in Queensland and the Northern Territory between 2012 and 2017.
Researchers found the vaccines were safe and did not increase the risk of preterm birth, stillbirth or small-for-gestational-age infants.
There was a 15 per cent lower risk of small babies in whooping cough vaccinated pregnancies in Queensland and a 22 per cent reduction in the risk of preterm birth in NT whooping cough vaccinated pregnancies.
There was also a seven per cent lower risk of preterm birth in Queensland influenza vaccinated pregnancies.
Medical and maternal communities had been calling for this research to help provide reassurance, lead author Kahlee Boyd said.
"Healthcare providers are crucial to influencing vaccine acceptance during pregnancy, and we want GPs to be able to tell patients there has been a local Australian study confirming the vaccines are safe," she said.
Women pregnant with multiples are often excluded from vaccine safety studies because they have a higher baseline risk of preterm birth and babies being small-for-gestational-age.
But these risk factors often mean twin babies have increased risk of vulnerability to the flu and whooping cough once they are born due to their lungs not being fully developed in utero.
"We are hoping that this study will show there is evidence that these vaccines are safe for twin pregnancies and we are hoping to increase vaccine uptake," she said.
But the gap in vaccine safety studies is not the only one impacting twin mums compared to those with singleton pregnancies.
Laura Wilson is a mum to four-year-old twins, but recalls her high-risk pregnancy left her with limited care options.
She says it's not an uncommon experience for women pregnant with multiples, which means many can fall through the cracks without continuity of care.
"I was quite limited in my choices of care and as a result I hired a private midwife who had a good relationship with the hospital which meant I could get consistency," she told AAP.
"If I didn't pay for that service I would have seen a different doctor or midwife every time (and) I would not have gotten the extra care I needed."
Now a board director at the Australian Multiple Birth Association, Ms Wilson advocates nationally for better support for multiple birth families.
Families can be overwhelmed when discovering they are expecting more than one baby and need better avenues for support, particularly within the healthcare system, she said.
"We need to consider multiples as being at the forefront rather than as an afterthought," she said.
"When multiple birth families are at the forefront of care options and research it means we can be more informed to make better choices for our family."
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