From about 24 weeks . I answered this from the "fetal" point of view. Here is my tap on babies' responses to noise: https://www.Healthtap.Com/user_questions/3622.
Birth. Babies can hear from within the womb.
For all preemie moms. I want to share something. A baby was born premature and had a hearing test before being discharged from the special care nursery. I'll never forget the young woman who said coldly, "he failed the test." weeks later he was retested, and a seasoned pro said he was ok & the 1st test was flawed by how she gave it. So ask for an expert's explanation or plan. It's not fair for you to worry for weeks.
Before birth. Babies are born hearing. They've been listening to you for months. Many states now require that your baby have their hearing checked before they even leave the nursery. Check with you birthing center or pediatrician to see if that is true in your state.
Early 2nd Trimester. Babies can hear well before they are born. Most babies can hear by 15-16 weeks gestation, so make sure that you talk to your baby, even while pregnant. Of course, babies can hear as soon as they are born. It's not until around 4 months that babies can localize to sound, meaning that they can turn their head in the direction that they hear the sound.
Right away. Your baby should be able to hear at birth and even before. Signs of hearing include startling to loud noises, calming her cry at the sound of your voice even before you are visible to her and showing preference to your voice over the voice of strangers. She will not be able to localize where a sound is coming from or respond to her name until she is several months old.
Before baby is born. Newborn hearing screen is mandated in a majority of the states in the US. Significant hearing can be missed by using behavior cues alone and undetected hearing loss can impair baby's acquisition of language skills and consequently affect academic, social and emotional development adversely. Any concerns about baby's hearing should be discussed with the healthcare provider as soon as possible.
Before your 1st kiss. In utero around the 8th month of pregnancy, before you first lay eyes on your newborn and before your first kiss, research shows babies can hear. Due to the importance hearing plays in developing overall healthy speech and well-being, hearing tests are performed in nurseries before a baby's discharge to detect early hearing problems right away. So, feel free to communicate and enjoy each other!
Birth. Your child's ability to hear develops before birth, and is well-attuned at recognizing the voices of its family right from the start. Of course, your baby is most accustomed to your voice, as well as the sound of your heartbeat, which accounts for why they calm so easily in your arms.
Womb. Babies should be able to hear from birth-- actually even in the womb they respond to noise. Most (not all) states require newborn hearing screening. To see if yours does, click on this link: http://www.Ncsl.Org/default.Aspx?Tabid=14382#state_laws.
Babies hear at birth. Babies can hear at birth. A baby can hear even before he is born, but the sounds are dampened because he is inside his mother and surrounded by amniotic fluid. Hearing tests can be done on newborns before discharge from the hospital.
Now. Many babies have hearing tests at birth - this determines if they have the hardware in their brains to hear. Babies will respond to sound immediately after birth but not all the time. Gradually, their hearing improves. If you don't see signs your baby can hear shortly after birth, check in with your doctor.
In utero... (before birth), most likely. Noises similar to heartbeat and stomach rumbling seem to calm colicky babies. Also, most states test hearing at birth, and very few children are identified as not being able to hear at birth.
Before birth!! Your baby's hearing is one of the earlier senses to develop, and they hear in-utero for months before they are born.They hear your heartbeat, your voice, and voices that mom hears frequently.You can actually watch a newborn alert to mom talking while ignoring unfamiliar voices in the room. Almost everywhere now tests your baby's hearing before he goes home, catching problems early.
Immediately. The baby's hearing is developed at birth. If there are no problems hearing tests can be done on day one and show normal hearing. What is lacking is the brain's ability to process the sound into meaning patterns recognized as speech. This is an ongoing process that develops from birth.
Right after birth. Babies can hear right after birth; they can even hear you when they are still in the womb. Most states require a hearing test soon after birth as part of their routine newborn screening assessment. These results can help confirm that he/she hears normally and should be carefully reviewed by your pediatrician with you.
Before s/he is born. Babies can hear even before birth. Music played before birth can often be very soothing to a crying baby after he/she is born.
In utero! Babies have finely developed hearing at birth, and even before! in fact, most babies are now screened in the hospital, after delivery, to pick up any hearing loss. Deafness or severe hearing loss can be hard to diagnosis without this screening. You will see that your newborn reacts to sounds, but can also "tune out" a lot of sounds and sleep right through them!
Now! Your baby's hearing has already developed while in the womb. Babies respond to sounds in utero and can even remember sounds they are exposed to. Before your baby leaves the hospital, he should have his hearing tested as part of a national effort to identify hearing loss early. If after having a normal hearing screen, your baby doesn't seem to respond to loud sounds, ask to have him retested.
From Birth. Hopefully, if all is healthy and well, from birth and really even before then.