Chanelle Watson started to spiral a few weeks before her daughter turned one.
"I think the emotions of new motherhood and juggling my work were catching up with me," she tells Essential Baby.
"I missed the simplicity of the newborn days, when it was just Charlotte and I at home. There were no daycare runs, no deadlines, no sitting in traffic. It hit me that it wasn't just us anymore. I felt like that was lost."
Things came to a head on Charlotte's first birthday, when Chanelle found herself wiping away tears as she watched her daughter open her presents.
"She was so active and she had the biggest smile on her face. I was like, 'Where's my baby gone?'"
Charlotte had started walking at 11 months, which made Chanelle, 26, even more conscious of the fact that her baby had become a toddler.
While the Melbourne mum says that she also felt joy and pride about her daughter's development and having made it through that tough first year, she became upset again when it was time to sing happy birthday.
Chanelle was later diagnosed with adjustment disorder and a mild case of postnatal depression. She says that she was putting herself under too much pressure at work and home, and that her daughter's first birthday triggered intense emotions.
This is not an uncommon experience for mums, says Central Coast psychotherapist Dr Karen Philip.
"Your child is changing rapidly in those three to four months before their first birthday. All of a sudden, we realise that our baby isn't a newborn anymore. They're growing up before our eyes."
Sydney-based psychologist Elizabeth Neal agrees, describing the conflicted feelings as "a necessary sense of loss."
"We didn't have a baby to keep a baby forever. But for the baby to grow up, we have to lose that baby phase. We have to let it go," she says.
The reason why the feeling of loss is 'necessary' is because it signals acceptance. It is denial that would be cause for concern, she says.
For many mums, the 12-month mark also means the end of maternity leave, which can be another reason to feel sad.
"You exist in a kind of cocoon that first year. It's tough at times, but also beautiful," says Neal. "Often, it's just you and your baby at home and you don't get out of your pyjamas until whatever-o'clock. You will never have that again, unless you go on to have more children. But even then, you'll have to juggle looking after the older one as well. So that first year is unique."
Neal says that mums can even experience a nostalgia that borders on being delusional – for example, forgetting the reflux and sleepless nights, or the sometimes-monotonous routine.
When to seek help
While it is healthy to feel some sadness about your baby's first birthday, those who start to experience anxiety should seek professional help.
"It is a little concerning when instead of sadness, there's anxiety," says Neal. "That is not helpful for a baby's development, or for us either. Because when our baby moves on, that's when we get to return to our goals and our ambitions. There's a mutual benefit to our baby growing up."
Both Neal and Philip say that sometimes women regret aspects of their behavior during that first year when they were tired and cranky, and worry that they have "stuffed their baby up."
"This can mean clinging to the past and wishing things had been different," says Neal.
The feeling never leaves you
Although many mums grieve the loss of babyhood as the first birthday approaches, it certainly isn't the last time that we will be struck by a sense of near panic that our child is growing up.
"Every milestone our child reaches, whether it be the first day of primary school, the first sleep-over, or even starting university, can make us think, 'Oh my goodness, my child doesn't need me like they used to.' That mixture of happy and sad feelings are with us throughout our lives," says Philip.
Neal has three children, and she says that moving onto each new stage can be a little bittersweet.
"My son is six and I miss the time we used to have at home before he started school. But now he comes home with awards and he writes me little love letters. This is new. And at some point, he's going to stop writing me love letters, and I'll be sad again. It's a constant cycle."
Another tip is to focus on the joy and pride you feel about your child transforming from a sleepy and squirmy newborn into an active and inquisitive child.
"When we're sad, we're self-focused," says Neal. "We need to look back at our child and realise that we have this new stage to enjoy. We have a toddler who is learning to walk and move objects with greater skill, and choosing certain foods over others. There's a little person developing."
And as for the big day itself, Neal suggests never forgetting why you are celebrating.
"It's far better to have a low-key birthday party than one that is as orchestrated as a corporate event and involves an incredible amount of stress. What is felt most by the child is the emotional climate of the household. If you're enjoying what you're doing, that's the best thing."